Spiral Matrix

Given an m x n matrix, return all elements of the matrix in spiral order.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [1,2,3,6,9,8,7,4,5]

Example 2:

Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

Solution 

import java.util.ArrayList;

import java.util.List;

class Solution {

public List<Integer> spiralOrder(int[][] matrix) {

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

if (matrix.length == 0) {

return result;

}

int top = 0; // Starting row

int bottom = matrix.length - 1; // Ending row

int left = 0; // Starting column

int right = matrix[0].length - 1; // Ending column

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

// Traverse from left to right across the top row

for (int j = left; j <= right; j++) {

result.add(matrix[top][j]);

}

top++;

// Traverse from top to bottom along the right column

for (int i = top; i <= bottom; i++) {

result.add(matrix[i][right]);

}

right--;

// Traverse from right to left across the bottom row (if any rows left)

if (top <= bottom) {

for (int j = right; j >= left; j--) {

result.add(matrix[bottom][j]);

}

bottom--;

}

// Traverse from bottom to top along the left column (if any columns left)

if (left <= right) {

for (int i = bottom; i >= top; i--) {

result.add(matrix[i][left]);

}

left++;

}

}

return result;

}

}