Episode 7 — DSA with JavaScript / 7.17 — Binary Search Tree

7.17.a — Binary Search Tree Operations & Algorithms

<< 7.17 Overview

What is a BST?

A Binary Search Tree maintains the property: for every node, all values in the left subtree are less, and all values in the right subtree are greater.

       8
      / \
     3   10
    / \    \
   1   6    14
      / \   /
     4   7 13

Inorder: [1, 3, 4, 6, 7, 8, 10, 13, 14] ← sorted!

BST Search

function search(root, target) {
    if (!root) return null;
    if (target === root.val) return root;
    if (target < root.val) return search(root.left, target);
    return search(root.right, target);
}

TreeNode* search(TreeNode* root, int target) {
    if (!root || root->val == target) return root;
    return target < root->val ? search(root->left, target) : search(root->right, target);
}

Time: O(h) where h = height. O(log n) balanced, O(n) skewed.

BST Insert

Insert 5 into:
       8
      / \
     3   10
    / \
   1   6

Compare: 5 < 8 → go left
         5 > 3 → go right
         5 < 6 → go left → insert here

       8
      / \
     3   10
    / \
   1   6
      /
     5

function insert(root, val) {
    if (!root) return new TreeNode(val);
    if (val < root.val) root.left = insert(root.left, val);
    else if (val > root.val) root.right = insert(root.right, val);
    return root;
}

TreeNode* insert(TreeNode* root, int val) {
    if (!root) return new TreeNode(val);
    if (val < root->val) root->left = insert(root->left, val);
    else if (val > root->val) root->right = insert(root->right, val);
    return root;
}

BST Delete

Three cases:

  1. Leaf node: Simply remove
  2. One child: Replace with child
  3. Two children: Replace with inorder successor (smallest in right subtree)
function deleteNode(root, key) {
    if (!root) return null;
    if (key < root.val) { root.left = deleteNode(root.left, key); }
    else if (key > root.val) { root.right = deleteNode(root.right, key); }
    else {
        if (!root.left) return root.right;
        if (!root.right) return root.left;
        let successor = root.right;
        while (successor.left) successor = successor.left;
        root.val = successor.val;
        root.right = deleteNode(root.right, successor.val);
    }
    return root;
}

Validate BST

function isValidBST(root, min = -Infinity, max = Infinity) {
    if (!root) return true;
    if (root.val <= min || root.val >= max) return false;
    return isValidBST(root.left, min, root.val) &&
           isValidBST(root.right, root.val, max);
}

Kth Smallest

function kthSmallest(root, k) {
    let count = 0, result = null;
    function inorder(node) {
        if (!node || result !== null) return;
        inorder(node.left);
        count++;
        if (count === k) { result = node.val; return; }
        inorder(node.right);
    }
    inorder(root);
    return result;
}

Convert sorted array to BST

function sortedArrayToBST(nums) {
    function build(lo, hi) {
        if (lo > hi) return null;
        const mid = Math.floor((lo + hi) / 2);
        const node = new TreeNode(nums[mid]);
        node.left = build(lo, mid - 1);
        node.right = build(mid + 1, hi);
        return node;
    }
    return build(0, nums.length - 1);
}

BST operations complexity

OperationBalancedSkewed
SearchO(log n)O(n)
InsertO(log n)O(n)
DeleteO(log n)O(n)
Min/MaxO(log n)O(n)

Advantages of BST

  1. Sorted order traversal in O(n)
  2. Efficient search/insert/delete: O(log n)
  3. Dynamic — no fixed size
  4. Floor/ceiling operations
  5. Range queries

Scenario bank (BST)

7.17a-001 — Find inorder successor (v1)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-002 — Find inorder predecessor (v2)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-003 — Convert BST to greater tree (v3)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-004 — Recover BST (two swapped) (v4)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-005 — Trim BST to range (v5)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-006 — Find closest value (v6)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-007 — BST iterator (next smallest) (v7)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-008 — Count nodes in range (v8)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-009 — Merge two BSTs (v9)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-010 — Convert BST to doubly linked list (v10)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-011 — Largest BST subtree (v11)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-012 — Unique BSTs (Catalan) (v12)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-013 — Balance a BST (v13)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-014 — Serialize BST (v14)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-015 — Two Sum in BST (v15)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-016 — Floor and ceiling in BST (v16)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-017 — Delete range from BST (v17)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-018 — Check if preorder is valid BST (v18)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-019 — Convert sorted list to BST (v19)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-020 — Find median in BST (v20)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-021 — Find inorder successor (v21)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-022 — Find inorder predecessor (v22)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-023 — Convert BST to greater tree (v23)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-024 — Recover BST (two swapped) (v24)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-025 — Trim BST to range (v25)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-026 — Find closest value (v26)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-027 — BST iterator (next smallest) (v27)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-028 — Count nodes in range (v28)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-029 — Merge two BSTs (v29)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-030 — Convert BST to doubly linked list (v30)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-031 — Largest BST subtree (v31)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-032 — Unique BSTs (Catalan) (v32)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-033 — Balance a BST (v33)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-034 — Serialize BST (v34)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-035 — Two Sum in BST (v35)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-036 — Floor and ceiling in BST (v36)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-037 — Delete range from BST (v37)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-038 — Check if preorder is valid BST (v38)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-039 — Convert sorted list to BST (v39)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-040 — Find median in BST (v40)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-041 — Find inorder successor (v41)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-042 — Find inorder predecessor (v42)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-043 — Convert BST to greater tree (v43)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-044 — Recover BST (two swapped) (v44)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-045 — Trim BST to range (v45)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-046 — Find closest value (v46)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-047 — BST iterator (next smallest) (v47)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-048 — Count nodes in range (v48)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-049 — Merge two BSTs (v49)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-050 — Convert BST to doubly linked list (v50)

  • Level: Beginner
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-051 — Largest BST subtree (v51)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-052 — Unique BSTs (Catalan) (v52)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-053 — Balance a BST (v53)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-054 — Serialize BST (v54)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-055 — Two Sum in BST (v55)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-056 — Floor and ceiling in BST (v56)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-057 — Delete range from BST (v57)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-058 — Check if preorder is valid BST (v58)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-059 — Convert sorted list to BST (v59)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-060 — Find median in BST (v60)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-061 — Find inorder successor (v61)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-062 — Find inorder predecessor (v62)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-063 — Convert BST to greater tree (v63)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-064 — Recover BST (two swapped) (v64)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-065 — Trim BST to range (v65)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-066 — Find closest value (v66)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-067 — BST iterator (next smallest) (v67)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-068 — Count nodes in range (v68)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-069 — Merge two BSTs (v69)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-070 — Convert BST to doubly linked list (v70)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-071 — Largest BST subtree (v71)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-072 — Unique BSTs (Catalan) (v72)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-073 — Balance a BST (v73)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-074 — Serialize BST (v74)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-075 — Two Sum in BST (v75)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-076 — Floor and ceiling in BST (v76)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-077 — Delete range from BST (v77)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-078 — Check if preorder is valid BST (v78)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-079 — Convert sorted list to BST (v79)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-080 — Find median in BST (v80)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-081 — Find inorder successor (v81)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-082 — Find inorder predecessor (v82)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-083 — Convert BST to greater tree (v83)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-084 — Recover BST (two swapped) (v84)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-085 — Trim BST to range (v85)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-086 — Find closest value (v86)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-087 — BST iterator (next smallest) (v87)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-088 — Count nodes in range (v88)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-089 — Merge two BSTs (v89)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-090 — Convert BST to doubly linked list (v90)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-091 — Largest BST subtree (v91)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-092 — Unique BSTs (Catalan) (v92)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-093 — Balance a BST (v93)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-094 — Serialize BST (v94)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-095 — Two Sum in BST (v95)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-096 — Floor and ceiling in BST (v96)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-097 — Delete range from BST (v97)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-098 — Check if preorder is valid BST (v98)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-099 — Convert sorted list to BST (v99)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-100 — Find median in BST (v100)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-101 — Find inorder successor (v101)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-102 — Find inorder predecessor (v102)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-103 — Convert BST to greater tree (v103)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-104 — Recover BST (two swapped) (v104)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-105 — Trim BST to range (v105)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-106 — Find closest value (v106)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-107 — BST iterator (next smallest) (v107)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-108 — Count nodes in range (v108)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-109 — Merge two BSTs (v109)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-110 — Convert BST to doubly linked list (v110)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-111 — Largest BST subtree (v111)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-112 — Unique BSTs (Catalan) (v112)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-113 — Balance a BST (v113)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-114 — Serialize BST (v114)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-115 — Two Sum in BST (v115)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-116 — Floor and ceiling in BST (v116)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-117 — Delete range from BST (v117)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-118 — Check if preorder is valid BST (v118)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-119 — Convert sorted list to BST (v119)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-120 — Find median in BST (v120)

  • Level: Intermediate
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-121 — Find inorder successor (v121)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-122 — Find inorder predecessor (v122)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-123 — Convert BST to greater tree (v123)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-124 — Recover BST (two swapped) (v124)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-125 — Trim BST to range (v125)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-126 — Find closest value (v126)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-127 — BST iterator (next smallest) (v127)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-128 — Count nodes in range (v128)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-129 — Merge two BSTs (v129)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-130 — Convert BST to doubly linked list (v130)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-131 — Largest BST subtree (v131)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-132 — Unique BSTs (Catalan) (v132)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-133 — Balance a BST (v133)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-134 — Serialize BST (v134)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-135 — Two Sum in BST (v135)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-136 — Floor and ceiling in BST (v136)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-137 — Delete range from BST (v137)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-138 — Check if preorder is valid BST (v138)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-139 — Convert sorted list to BST (v139)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-140 — Find median in BST (v140)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-141 — Find inorder successor (v141)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-142 — Find inorder predecessor (v142)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-143 — Convert BST to greater tree (v143)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-144 — Recover BST (two swapped) (v144)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-145 — Trim BST to range (v145)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-146 — Find closest value (v146)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-147 — BST iterator (next smallest) (v147)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-148 — Count nodes in range (v148)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-149 — Merge two BSTs (v149)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-150 — Convert BST to doubly linked list (v150)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-151 — Largest BST subtree (v151)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-152 — Unique BSTs (Catalan) (v152)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-153 — Balance a BST (v153)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-154 — Serialize BST (v154)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-155 — Two Sum in BST (v155)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-156 — Floor and ceiling in BST (v156)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-157 — Delete range from BST (v157)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-158 — Check if preorder is valid BST (v158)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-159 — Convert sorted list to BST (v159)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-160 — Find median in BST (v160)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-161 — Find inorder successor (v161)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-162 — Find inorder predecessor (v162)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-163 — Convert BST to greater tree (v163)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-164 — Recover BST (two swapped) (v164)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-165 — Trim BST to range (v165)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-166 — Find closest value (v166)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-167 — BST iterator (next smallest) (v167)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-168 — Count nodes in range (v168)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-169 — Merge two BSTs (v169)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.

7.17a-170 — Convert BST to doubly linked list (v170)

  • Level: Advanced
  • Approach: Apply technique.
  • Time/Space: Analyze.
  • Edge cases: empty, single, boundary.
  • JS & C++: Both.