一、题目

二、代码

class Solution {
    
public:
    vector<vector<int>> generateMatrix(int n) {
    

     //Seems to have found a pattern
     //The law of subtraction is once-1 -1 -2 -2 -3 -3 -4 -4 When the subtraction is 0 时停止
      vector<vector<int> > return_vector(n, vector<int>(n, 0));  
      
      //常规变量
      int i=0;
      int j=0;
      int k=0;

      //本题变量
      int x=0;          //x和y Controls the change of subscripts,范围都是0-n-1 x代表行 y 代表列
      int y=0;
      
      int count_decrease=0;
      int maxlength=n-1;
      int fill_num=1; //依次填充


      int direction=1; //direction number 1表示右 2表示下 3表示左 4表示上 状态轮转

      for(y=0;y<=n-1;y++)         //The first line is not in the pattern Fill individually 这里y会多加一次 需要减掉
      {
    
       return_vector[x][y]=fill_num;
       fill_num=fill_num+1;
      }

      y=y-1;     //将y恢复到n-1 
 
      //Fill in the following according to the rules
     while(fill_num<=n*n)
     {
    
       direction=direction+1;  //方向改变
       if(direction==5)  direction=1;

        count_decrease=count_decrease+1;
       if(count_decrease==3) 
       {
    
        count_decrease=1;
        maxlength=maxlength-1;
       }


       if(direction==1)    //向右
       {
    
             for(i=1;i<=maxlength;i++)
         {
    
            // std::cout<<" fill num "<<fill_num<<" "<<" max length "<<maxlength<<std::endl;
              y=y+1;
              return_vector[x][y]=fill_num;
              fill_num=fill_num+1;

         }
       }

       if(direction==2)  //向下
       {
    
           for(i=1;i<=maxlength;i++)
         {
    
           // std::cout<<" fill num "<<fill_num<<" "<<" max length "<<maxlength<<std::endl;
              x=x+1;
              return_vector[x][y]=fill_num;
              fill_num=fill_num+1;
          
         }

       }

        if(direction==3)  //向左
       {
    
            for(i=1;i<=maxlength;i++)
         {
    
            // std::cout<<" fill num "<<fill_num<<" "<<" max length "<<maxlength<<std::endl;
              y=y-1;
              return_vector[x][y]=fill_num;
              fill_num=fill_num+1;
             
         }
       }

        if(direction==4)  //向上
       {
    
            for(i=1;i<=maxlength;i++)
         {
    
             // std::cout<<" fill num "<<fill_num<<" "<<" max length "<<maxlength<<std::endl;
              x=x-1;
              return_vector[x][y]=fill_num;
              fill_num=fill_num+1;
              
         }
       }
     }
      return return_vector;
    }
};

三、运行结果