Episode 7 — DSA with JavaScript / 7.8 — Advanced Array Problems

7.8 — Quick Revision: Advanced Arrays

<< Overview

Key techniques

TechniqueWhen to useTime
Two pointers (opposite)Sorted array, pair findingO(n)
Two pointers (same dir)Sliding window, fast/slowO(n)
Prefix sumRange queries, subarray sumsO(n) build, O(1) query
Variable sliding windowSubstring/subarray with constraintO(n)
Matrix traversalSpiral, diagonal, zigzagO(m×n)

Matrix operations

OperationMethodTime
Rotate 90°Transpose + reverse rowsO(n²)
Spiral order4 boundariesO(m×n)
Search sortedBinary search (1D mapping)O(log mn)
Set zeroesFirst row/col as markersO(mn), O(1) space

Self-check drill

SC-001

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-002

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-003

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-004

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-005

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-006

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-007

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-008

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-009

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-010

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-011

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-012

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-013

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-014

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-015

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-016

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-017

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-018

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-019

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-020

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-021

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-022

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-023

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-024

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-025

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-026

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-027

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-028

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-029

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-030

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-031

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-032

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-033

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-034

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-035

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-036

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-037

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-038

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-039

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-040

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-041

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-042

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-043

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-044

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-045

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-046

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-047

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-048

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-049

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-050

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-051

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-052

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-053

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-054

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-055

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-056

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-057

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-058

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-059

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-060

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-061

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-062

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-063

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-064

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-065

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-066

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-067

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-068

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-069

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-070

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-071

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-072

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-073

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-074

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-075

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-076

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-077

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-078

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-079

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-080

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-081

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-082

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-083

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-084

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-085

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-086

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-087

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-088

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-089

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-090

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-091

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-092

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-093

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-094

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-095

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-096

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-097

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-098

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-099

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-100

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-101

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-102

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-103

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-104

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-105

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-106

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-107

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-108

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-109

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-110

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-111

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-112

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-113

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-114

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-115

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-116

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-117

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-118

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-119

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-120

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-121

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-122

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-123

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-124

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-125

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-126

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-127

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-128

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-129

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-130

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-131

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-132

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-133

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-134

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-135

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-136

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-137

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-138

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-139

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-140

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-141

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-142

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-143

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-144

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-145

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-146

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-147

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-148

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-149

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-150

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-151

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-152

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-153

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-154

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-155

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-156

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-157

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-158

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-159

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-160

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-161

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-162

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-163

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-164

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-165

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-166

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-167

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-168

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-169

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-170

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-171

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-172

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-173

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-174

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-175

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-176

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-177

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-178

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-179

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-180

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-181

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-182

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-183

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-184

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-185

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-186

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-187

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-188

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-189

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-190

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse

SC-191

  • Q: Container water approach?
  • A: Two pointers, move shorter side

SC-192

  • Q: 3Sum avoid duplicates?
  • A: Sort, skip same values

SC-193

  • Q: Prefix sum for range?
  • A: prefix[r] - prefix[l-1]

SC-194

  • Q: Spiral traverse?
  • A: 4 boundaries, shrink after each direction

SC-195

  • Q: Rotate matrix?
  • A: Transpose + reverse rows

SC-196

  • Q: Search sorted 2D?
  • A: Binary search on flattened index

SC-197

  • Q: Min window substring?
  • A: Variable window + frequency maps

SC-198

  • Q: Sliding window max?
  • A: Deque maintaining max candidates

SC-199

  • Q: Merge intervals?
  • A: Sort by start, extend overlapping

SC-200

  • Q: Next permutation?
  • A: Find rightmost ascent, swap ceiling, reverse