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 ]
]
思路：这道题顺时针从1到n2放入数组，没啥高深数据结构或算法，直接顺时针打印就可以了。

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
        vector<vector<int> > matrix(n,vector<int>(n));
        if(n<=0)
            return matrix;
        int sum=1;
        int start=0;
        while(start<(n+1)/2)
        {
            for(int i=start;i<=n-1-start;i++)
            {
                matrix[start][i]=sum++;
            }
            for(int i=start+1;i<=n-1-start;i++)
            {
                matrix[i][n-1-start]=sum++;
            }
            for(int i=n-2-start;i>=start;i--)
            {
                matrix[n-1-start][i]=sum++;
            }
            for(int i=n-2-start;i>=start+1;i--)
            {
                matrix[i][start]=sum++;
            }
            start++;
        }
        return matrix;
    }
};