视频讲解中的思路图解

代码

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> result = new ArrayList();
        if(matrix == null || matrix.length < 1) return result;

        int m = matrix.length, n = matrix[0].length;
        int[] dx = {0,1,0,-1}, dy = {1,0,-1,0};
        boolean[][] used = new boolean[m][n];

        for(int i = 0, x = 0, y = 0, d = 0; i < m * n; i++){
            result.add(matrix[x][y]);
            used[x][y] = true;

            //检验下一个位置是否合法, 不合法则更新方向, 并重新计算下一个位置
            int a = x + dx[d], b = y + dy[d];
            if( a < 0 || a >= m || b < 0 || b >= n || used[a][b]){
                d ++;
                d %= 4;

                a = x + dx[d];
                b = y + dy[d];
            }

            x = a ;
            y = b;
        }

        return result;
    }
}