[LeedCode OJ]#59 Spiral Matrix II

class Solution
{
public:
    vector<vector<int> > generateMatrix(int n)
    {
        vector<vector<int> > a;
        if(n==0)
            return a;
        a.resize(n);
        for(int i = 0; i<n; i++)
            a[i].resize(n);
        int e = 1;
        int x = 0,y = 0;
        while(e<=n*n)
        {
            while(y<n&&e<=n*n&&!a[x][y]) a[x][y++] = e++;
            x++,y--;
            while(x<n&&e<=n*n&&!a[x][y]) a[x++][y] = e++;
            x--,y--;
            while(y>=0&&e<=n*n&&!a[x][y]) a[x][y--] = e++;
            y++,x--;
            while(x>=0&&e<=n*n&&!a[x][y]) a[x--][y] = e++;
            x++,y++;
        }
    }
};