给定一个正整数 n，生成一个包含 1 到 n2 所有元素，且元素按顺时针顺序螺旋排列的正方形矩阵。

示例:

输入: 3 输出: [ [ 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, 0));

        int left = 0;

        int up = 0;

        int right = n - 1;

        int down = n - 1;

        int cnt = 1;

        while(up <= down && left <= right)

        {

            for(int i = left; i <= right; i++)

                res[up][i] = cnt++;

            up++;

            if(up > down)

                break;

            for(int i = up; i <= down; i++)

                res[i][right] = cnt++;

            right--;

            if(left > right)

                break;

            for(int i = right; i >= left; i--)

                res[down][i] = cnt++;

            down--;

            if(up > down)

                break;

            for(int i = down; i >= up; i--)

                res[i][left] = cnt++;

            left++;

            if(left > right)

                break;

        }

        return res;

    }

};