[leetcode]Spiral Matrix II

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(n == 0) return vector<vector<int>>();
        vector<vector<int>> f(n, vector<int>(n,0));
        
        int cnt = 1;
        for(int start = 0; start < n/2; start++){
            for(int j = start; j < n-start; j++){
                f[start][j] = cnt;
                cnt++;
            }
            for(int i = start+1; i < n-1-start; i++){
                f[i][n-1-start] = cnt;
                cnt++;
            }
            for(int j = n-1-start; j >= start; j--){
                f[n-1-start][j] = cnt;
                cnt++;
            }
            for(int i = n-1-start-1; i>start; i--){
                f[i][start] = cnt;
                cnt++;
            }
            
        }
        
        if(n%2 != 0){
            f[n/2][n/2] = cnt;
        }
    
        return f;    
    }
};