59. Spiral Matrix II

同Spiral Matrix一样，我们也是逐个环地进行填充，每个环顺时针逐条边填充。代码如下：

class Solution {public:    vector<vector<int>> generateMatrix(int n) {        vector<vector<int>> res(n, vector<int>(n));        int cycle = (n+1)/2, num=1;        for (int i=0; i<cycle; i++) { // i代表第几个环            // 每个环的左上角起点是matrix[i][i],下面顺时针依次填充环的四条边            for (int j=i; j<n-i; j++) {                res[i][j]=num++;            }            for (int j=i+1; j<n-i; j++) {                res[j][n-i-1] = num++;            }                        for (int j=n-i-2; j>=i; j--) {                res[n-i-1][j] = num++;            }            for (int j=n-i-2; j>i; j--) {                res[j][i] = num++;            }        }        return res;    }};