[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 ]
]

思考：ACM蛇形填数。

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