(三)剑指offer 43翻转单词顺序列

“student. a am I”-----》“I am a student.”

思路：反转字符串的思路

1. 反转整个字符串
2. 反转每个单词

class Solution {
 void my_reverse(string &str,int left,int right)
 {
     if(left>=right)return ;
     while(left<right)
     {
          swap(str[left++],str[right--]);   
     }
 }
public:
    string ReverseSentence(string str) 
    {
        int n=str.size();
        if(n==0)return "";
        reverse(str.begin(),str.end());
        int start=0,end=0;
        int i=0;
        while(i<n)
        {
            while(i<n&&str[i]==' ')
                i++;
            start=end=i;
            while(i<n&&str[i]!=' ')
            {
                i++;
                end++;
            }
            end-=1;
            my_reverse(str,start,end);
        }
        return str;
    }
};