Matrix problems often look intimidating.

Too many rows, columns, indices…

But most interview questions are built on just a few core patterns.

Master these patterns once,

and matrix questions become much easier.

1. Spiral Traversal

Problem

Print matrix elements in spiral order.

public static List spiralOrder(int[][] matrix) {

List<Integer> result = new ArrayList<>();

int top = 0, bottom = matrix.length - 1; int left = 0, right = matrix[0].length - 1;

while (top <= bottom && left <= right) {

for (int i = left; i <= right; i++) result.add(matrix[top][i]);

top++;

for (int i = top; i <= bottom; i++) result.add(matrix[i][right]);

right--;

if (top <= bottom) { for (int i = right; i >= left; i--) result.add(matrix[bottom][i]);

bottom--; }

if (left <= right) { for (int i = bottom; i >= top; i--) result.add(matrix[i][left]);

left++; } }

return result;

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}

Core Idea

Maintain 4 boundaries:

top

bottom

left

right

Move inward layer by layer.

2.…