leetcode题集——spiral-matrix-ii

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

For example,
Given n =3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) 
    {
      vector<vector<int> > ret(n,vector<int>(n,0));//二维容器的初始化
      int start=0;
      int end=n-1;
      int sum=1;
        
      while(start<end)
      {
         for(int j=start;j<end;j++)
         {
            ret[start][j]=sum;
             sum++;
         }
         for(int i=start;i<end;i++)
         {
            ret[i][end]=sum;
             sum++;
         }
        for(int j=end;j>start;j--)
         {
             ret[end][j]=sum;
             sum++;
         }
         for(int i=end;i>start;i--)
         {
             ret[i][start]=sum;
             sum++;
         }
          start++;
          end--;
      }
        if(start==end)
            ret[start][end]=sum;
        return ret;
    }
};