Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order.

For example,

Given n = 3,

You should return the following matrix:

[

[ 1, 2, 3 ],

[ 8, 9, 4 ],

[ 7, 6, 5 ]

]


思路：

转圈向里赋值，注意边界条件即可。

代码：

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
        int half = n/2, cnt = 1;
        vector<vector<int> > ret(n, vector<int>(n, 0));
        for(int m = 0; m < half; ++m){
            for(int i = m; i < n - m - 1; ++i){
                ret[m][i] = cnt;
                ++cnt;
            }
            for(int i = m; i < n - m - 1; ++i){
                ret[i][n-m-1] = cnt;
                ++cnt;
            }
            for(int i = n - m - 1; i > m; --i){
                ret[n-m-1][i] = cnt;
                ++cnt;
            }
            for(int i = n - m - 1; i > m; --i){
                ret[i][m] = cnt;
                ++cnt;
            }
        }
        if(n % 2 == 1) ret[n/2][n/2] = n*n;
        return ret;
    }
};