https://leetcode-cn.com/problems/spiral-matrix-ii/
Idea: Yesterday the code was changed and it was done.
class Solution {
public:
vector<vector<int>> generateMatrix(int n) {
vector<vector<int>> ans(n,vector<int>(n));
int left=0,right=n-1,top=0,down=n-1,val=0;
while(left<=right&&top<=down)
{
for(int i=left;i<=right;i++)
ans[top][i]=++val;
++top;
for(int i=top;i<=down;i++)
ans[i][right]=++val;
--right;
for(int i=right;i>=left;i--)
ans[down][i]=++val;
--down;
for(int i=down;i>=top;i--)
ans[i][left]=++val;
++left;
}
return ans;
}
};