Reverse Words in a String

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

click to show clarification.

Clarification:

 

• What constitutes a word?
  A sequence of non-space characters constitutes a word.
• Could the input string contain leading or trailing spaces?
  Yes. However, your reversed string should not contain leading or trailing spaces.
• How about multiple spaces between two words?
  Reduce them to a single space in the reversed string.

经典的题目，注意题中的空格问题，首尾不能有空格，也不能有连续的空格

class Solution {
public:
    void trim(string &s){
      //去除首尾空格
      s.erase(s.begin(),find_if(s.begin(),s.end(),[](char c){return c!=' ';}));
      s.erase(find_if(s.rbegin(),s.rend(),[](char c){return c!=' ';}).base(),s.end());
      //去除重复空格
      s.erase(unique(s.begin(),s.end(),[](char l,char r){return l==r && l==' ';}),s.end());
    }
    void reverseWords(string &s) {
        std::reverse(s.begin(),s.end());
        string::iterator wordBegin = s.begin();
        while(wordBegin<s.end()){
            string::iterator spaceIta =  find(wordBegin,s.end(),' ');
            reverse(wordBegin,spaceIta);
            wordBegin = spaceIta+1;
        }
        trim(s);
    }
};