Spiral Matrix II

问题：蛇形矩阵
分析：设置变量dir，0123分别代表方向右下左上

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class Solution { public:     int num[300][300];     void dfs(int x,int y,int k,int n,int dir)     {         num[x][y]=k;         if(k>=n*n) return ;//这里要用大于,n=0会一直不出现等于         if(dir==0)         {             if(y+1<n && num[x][y+1]==0 ) dfs(x,y+1,k+1,n,0);             else dfs(x+1,y,k+1,n,1);//如果右边不能走，就走下边         }         if(dir==1)         {             if( x+1<n && num[x+1][y]==0) dfs(x+1,y,k+1,n,1);             else dfs(x,y-1,k+1,n,2);         }         if(dir==2)         {             if(y-1>=0 && num[x][y-1]==0) dfs(x,y-1,k+1,n,2);             else dfs(x-1,y,k+1,n,3);         }         if(dir==3)         {             if(x-1>=0 && num[x-1][y]==0) dfs(x-1,y,k+1,n,3);             else dfs(x,y+1,k+1,n,0);         }     }     vector<vector<int> > generateMatrix(int n) {        // memset(num,0,sizeof(num));         vector<vector<int> >vec1;        dfs(0,0,1,n,0);         for(int i=0;i<n;i++)         {             vector<int> vec2;             for(int j=0;j<n;j++)             {                 vec2.push_back(num[i][j]);             }             vec1.push_back(vec2);         }         return vec1;     } };