Spiral Matrix

题目：

Given a matrix of m ✕ n elements (m rows, n columns), return all elements of the
matrix in spiral order.
For example, given the following matrix:
[
[ 1, 2, 3 ],
[ 4, 5, 6 ],
[ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5]

解答：

public class Solution {
    public static void main(String[] args) {
        int[][] matrix = {{1,2,3},{4,5,6},{7,8,9}};
        List<Integer> elements = spiralOrder(matrix);
    }

    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> elements = new ArrayList<>();

        if(matrix.length == 0) {
            return elements;
        }

        int m = matrix.length;
        int n = matrix[0].length;
        int row = 0;
        int col = -1;

        while(true) {
            for(int i = 0; i < n; i++) {
                elements.add(matrix[row][++col]);
            }

            if(--m == 0) {
                break;
            }

            for(int i = 0; i < m; i++) {
                elements.add(matrix[++row][col]);
            }

            if(--n == 0) {
                break;
            }

            for(int i = 0; i < n; i++) {
                elements.add(matrix[row][--col]);
            }

            if(--m == 0) {
                break;
            }

            for(int i = 0; i < m; i++) {
                elements.add(matrix[--row][col]);
            }

            if(--n == 0) {
                break;
            }
        }

        return elements;
    }
}