leetcode(54)螺旋矩阵

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> list = new ArrayList<>();
        int xlen = matrix.length;
        if(xlen==0||matrix[0].length==0){
            return list;
        }
        int ylen = matrix[0].length;
        int i = 0;
        int j = ylen-1;
        int m = xlen-1;
        int n = 0;
        while(i<=m&&n<=j){
            for(int k=n;k<=j;++k){
                list.add(matrix[i][k]);
            }
            ++i;
            if(n<=j){
                for(int k=i;k<=m;++k){
                    list.add(matrix[k][j]);
                }
            }
            --j;
            if(i<=m){
                for(int k=j;k>=n;--k){
                    list.add(matrix[m][k]);
                }
            }
            --m;
            if(n<=j){
                for(int k=m;k>=i;--k){
                    list.add(matrix[k][n]);
                }
            }
            ++n;
        }
        return list;
    }
}