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 ]
]
ps：判断好边界即可，n为偶数或者奇数，都是走n/2圈。
n为奇数的时候，要记得给n*n矩阵正中间剩下那个值赋值。
代码：

class Solution{
private:
    int num;
public:
    void doit(int start,int end,vector<vector<int>>& res){
        if(start>=end) return;
        int col;int row;col=row=end;
        for (int i=start;i<=col;++i) res[start][i]=num++;
        for (int j=start+1;j<=row;++j) res[j][col]=num++;
        for (int m=col-1;m>=start;--m) res[row][m]=num++;
        for (int n=row-1;n>=start+1;--n) res[n][start]=num++;
        return;
    }
    vector<vector<int> > generateMatrix(int n) {
        vector<int> temp(n,0);
        vector<vector<int> > res(n,temp);
        if(n<=0) return res;
        num=1;
        int time=n/2;
        for (int i=0;i<time;++i)
        {
            doit(i,n-1-i,res);
        }
        if(n==1) 
            res[0][0]=1;
        else if(n>=3&&n&0x1==1)
            res[time][time]=n*n;
        return res;
    }
};