# 59.Spiral Matrix II

**59.Spiral Matrix II**

难度:Medium

> Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

```
Input: 3
Output:
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]
```

从起点位置开始，一次连续放置数字，到头了或者前面的数字已经被放过了，则开始转向。建立一个方向向量，每次到头换一次，知道所有的`n*n`个数被放满。

```
class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int>> res(n,vector<int>(n,0));
        res[0][0]=1;
       // if(n==1) return  res;
        int cur=2;
        vector<vector<int>> direct={{0,1}, {1,0},{0,-1}, {-1,0}};
        vector<int > start = {0,0};
        vector<int> p=direct[0];
        int pr=0;
        int N=n*n;
        while(cur<=N) 
        {
            int indx = start[0]+p[0] ;
            int indy = start[1]+p[1] ;
           // cout<<cur<<"  "<< start[0]+p[0] << "  "<<start[1]+p[1]<<endl;
            if(indx<0 || indx >=n || indy <0 || indy >=n || res[indx][indy] )
            {
                pr = (pr+1)%4;
                p = direct[pr];

            }
            else
            {
                res[indx][indy] =cur++;
                start[0]=indx;
                start[1] = indy;

            }


        }
        return res;
        
    }
};
```

> 执行用时 :8 ms, 在所有 C++ 提交中击败了68.59%的用户\
> 内存消耗 :9 MB, 在所有 C++ 提交中击败了42.07%的用户


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