dsa2 min read
Spiral Matrix — Direction Array Simulation [Google, Meta, Amazon]
Return all elements of an m×n matrix in spiral order. Use boundary shrinking or direction array. O(m*n) time O(1) space.
Read →
Matrix
8 articles
dsa1 min read
Rotate Image 90 Degrees — Transpose + Flip O(n²) [Meta, Google]
Rotate an n×n matrix 90 degrees clockwise in-place. Trick: transpose (swap i,j with j,i) then reverse each row. O(n²) time O(1) space.
Read →
dsa1 min read
Kth Smallest Element in a Sorted Matrix — Binary Search on Value
Find the kth smallest element in a row-column sorted matrix by binary searching on the value range.
Read →
dsa2 min read
Equal Row and Column Pairs — Hash Tuple Rows and Columns
Count (row, col) pairs that are equal by hashing each row tuple and each column tuple.
Read →
dsa1 min read
Maximal Rectangle — Histogram Stack on Each Row
Find the maximal rectangle in a binary matrix by building histogram heights row by row and applying largest rectangle.
Read →
dsa3 min read
Matrix Exponentiation: Fibonacci and Linear Recurrences
Solve linear recurrences like Fibonacci in O(log n) using matrix exponentiation. Essential for DP optimization on large n.
Read →
dsa2 min read
Google — Staircase Search in Row-Column Sorted Matrix
Search for a target in a matrix where each row and column is sorted. O(m+n) solution using top-right corner elimination — a classic Google interview problem.
Read →
dsa2 min read
Google — Trapping Rain Water II (3D BFS + Min-Heap)
Calculate how much water can be trapped in a 3D height matrix. Uses a min-heap BFS starting from the boundary, always processing the lowest border cell to determine water trapped inside.
Read →