_54.java

package com.fishercoder.solutions;

import java.util.ArrayList;
import java.util.List;

public class _54 {

    public static class Solution1 {
        /**
         * credit: https://leetcode.com/problems/spiral-matrix/discuss/20599/Super-Simple-and-Easy-to-Understand-Solution/185257
         */
        public List<Integer> spiralOrder(int[][] matrix) {
            if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
                return new ArrayList<>();
            }
            int m = matrix.length;
            int n = matrix[0].length;
            List<Integer> result = new ArrayList();
            int left = 0;
            int right = n - 1;
            int top = 0;
            int bottom = m - 1;
            while (result.size() < m * n) {
                for (int j = left; j <= right && result.size() < m * n; j++) {
                    result.add(matrix[top][j]);
                }
                top++;
                for (int i = top; i <= bottom && result.size() < m * n; i++) {
                    result.add(matrix[i][right]);
                }
                right--;
                for (int j = right; j >= left && result.size() < m * n; j--) {
                    result.add(matrix[bottom][j]);
                }
                bottom--;
                for (int i = bottom; i >= top && result.size() < m * n; i--) {
                    result.add(matrix[i][left]);
                }
                left++;
            }
            return result;
        }
    }
}