Matrix

Navigate 2D grids with DFS/BFS, rotation, spiral traversal, and flood fill.

7 problems 1 Easy 6 Medium 0 Hard

Overview

Matrix problems are essentially graph problems on a 2D grid. The standard pattern is to treat each cell as a node and its 4 (or 8) neighbors as edges.

When to Use

Rotate image 90°
Spiral matrix traversal
Set matrix zeros
Search a 2D matrix
Surrounded regions
Game of life

Common Mistakes

Boundary checks — always verify r >= 0, r < rows, c >= 0, c < cols
Modifying the matrix while traversing causes bugs — use a copy or temp marker
Forgetting diagonal neighbors when 8-directional movement is needed

Complexity

Time

O(m × n)

Space

O(m × n) for BFS/DFS, O(1) for in-place tricks

const DIRS = [[1,0],[-1,0],[0,1],[0,-1]];

function bfsGrid(grid, startR, startC) {
  const rows = grid.length, cols = grid[0].length;
  const queue = [[startR, startC]];
  const visited = new Set([`${startR},${startC}`]);

  while (queue.length) {
    const [r, c] = queue.shift();
    for (const [dr, dc] of DIRS) {
      const nr = r + dr, nc = c + dc;
      const key = `${nr},${nc}`;
      if (nr >= 0 && nr < rows && nc >= 0 && nc < cols && !visited.has(key)) {
        visited.add(key);
        queue.push([nr, nc]);
      }
    }
  }
}

Problems (7)

Hide completed

Problem	Difficulty	Companies	Freq
Rotate Image	Medium	AmazonMicrosoft +1	High
Spiral Matrix	Medium	AmazonMicrosoft +2	High
Set Matrix Zeroes	Medium	AmazonMicrosoft +1	High
Maximal Square	Medium	FacebookAmazon +2	High
Game of Life	Medium	GoogleAmazon +2	Medium
Search a 2D Matrix II	Medium	AmazonApple +2	High
Count Negative Numbers in a Sorted Matrix	Easy	AmazonGoogle	Medium

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