leetcode 59. 螺旋矩阵 II

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] res = new int[n][n];
        int flag = 1; 
        int p =0,q=0;  
        for (int i = 0; i < n*n; i++) {
            res[p][q] = i+1;
            if (flag == 1) {  
                q++;
                if (q>=n || res[p][q]!=0) {
                    flag++;
                    q--;
                    p++;
                }
            } else if (flag == 2) {  
                p++;
                if (p>=n || res[p][q]!=0) {
                    flag++;
                    p--;
                    q--;
                }
            } else if (flag == 3) {    
                q--;
                if (q<0 || res[p][q]!=0) {
                    flag++;
                    q++;
                    p--;
                }
            } else if (flag == 4) {    
                p--;
                if (p<0 || res[p][q]!=0) {
                    flag=1;
                    p++;
                    q++;
                }
            }
        }
        return res;
    }
}