LeetCode 螺旋矩阵

给定一个包含 m x n 个元素的矩阵（m 行, n 列），请按照顺时针螺旋顺序，返回矩阵中的所有元素。

示例 1:

输入:
[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
输出: [1,2,3,6,9,8,7,4,5]


示例 2:

输入:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
输出: [1,2,3,4,8,12,11,10,9,5,6,7]

题解

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        if (matrix.length == 0) {
            return new ArrayList<>(0);
        }
        int M = matrix.length;
        int N = matrix[0].length;
        List<Integer> list = new ArrayList<>(M * N);
        int i,j;
        int p = M, q = N;
        int m = 0;
        while(p>0 && q>0) {
            i = m; j= m;
            while(j<=N-m-1) list.add(matrix[i][j++]);
            i = i+1; j = N-m-1;
            while(i<=M-m-1) list.add(matrix[i++][j]);
            i = M-m-1; j=j-1;
            while(i>m && j>=m) list.add(matrix[i][j--]);
            i = i-1; j=m;
            while(i>m && j<N-m-1) list.add(matrix[i--][j]);
            m++;
            p-=2;
            q-=2;
        }
        return list;
    }
}