59. Spiral Matrix II

/*Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.For example,Given n = 3,You should return the following matrix:[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ]]*/class Solution {public:    vector<vector<int>> generateMatrix(int n) {        vector<vector<int>> res(n,vector<int>(n));int row_u = 0,row_d=n-1,column_l=0,column_r=n-1;int k=1;while(k <= n*n){for(int i=column_l;i<=column_r;i++)//上面一行res[row_u][i]=k++;row_u++;for(int i=row_u;i<=row_d;i++)//右边一列res[i][column_r]=k++;column_r--;for(int i=column_r;i>=column_l;i--)//下面一行res[row_d][i]=k++;row_d--;for(int i=row_d;i>=row_u;i--)//左边一列res[i][column_l]=k++;column_l++;}return res;    }};