Leetcode 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 dx[] = {,,,-};
        int dy[] = {,,-,};
        int cnt = ,step = ,x =  , y = ;
        while(cnt <= n*n){
            step%=;
            res[x][y] = cnt++;
            if(x+dx[step] >=n || x+dx[step] <  || y+dy[step] >=n || y+dy[step] <  || res[x+dx[step]][y+dy[step]]) step++;
            x+=dx[step%];y+=dy[step%];
        }
        return res;
    }
};