59-螺旋矩阵2

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int>> m(n,vector<int>(n,0)); 
        int num=1;
        int left=0,right=n-1,up=0,down=n-1;
        while(num<=n*n)
        {
            for(int i=left;i<=right;i++)       //从左到右依次赋值
            {
                m[up][i]=num++;
            }
            up++;                             //上面的行满了，所以顶要加一向下走
            for(int i=up;i<=down;i++)         //从右到下依次赋值
            {
                m[i][right]=num++;
            }
            right--;
            for(int i=right;i>=left;i--)      //从右到左
            {
                m[down][i]=num++;
            }
            down--;
            for(int i=down;i>=up;i--)         //从下到上
            {
                m[i][left]=num++;
            }
            left++;
            
        }
        return m;

    }
};