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;    }};