Spiral Matrix

Problem

Given an m × n matrix, return all elements in spiral order — clockwise from the top-left, peeling off the outer layer at each step.

Constraints

• 1 ≤ m, n ≤ 10

Approach — Core Patterns

This is a Core Patterns problem. The idea: pick the data structure best matched to the constraints and solve it in one clean pass. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: see the walkthrough below.

Solution code

Python

class Solution:
    def spiralOrder(self, matrix):
        res = []
        while matrix:
            res += matrix.pop(0)
            matrix = [list(r) for r in zip(*matrix)][::-1]
        return res

Java

import java.util.*;

class Solution {
    public List<Integer> spiralOrder(int[][] m) {
        List<Integer> out = new ArrayList<>();
        int top = 0, bot = m.length - 1, l = 0, r = m[0].length - 1;
        while (top <= bot && l <= r) {
            for (int j = l; j <= r; j++) out.add(m[top][j]);
            top++;
            for (int i = top; i <= bot; i++) out.add(m[i][r]);
            r--;
            if (top <= bot) { for (int j = r; j >= l; j--) out.add(m[bot][j]); bot--; }
            if (l <= r)     { for (int i = bot; i >= top; i--) out.add(m[i][l]); l++; }
        }
        return out;
    }
}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.