reverse word in a string（leetcode）

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.
• 方法就是先将整个string翻转，然后再将多余空格变为一个空格，在将其中每个单词翻转即可。
• 我为了避免调整空格的繁琐移动操作，就直接另建一string，保留每个word的翻转结果，最后将其赋值给s即可
  

  class Solution {public:    void reverseWords(string &s) {        if( s.empty() ){ return; }reverse( s.begin(),s.end() );string::iterator left = s.begin(),right = s.begin();enum{ OFF,ON } state;state = OFF;string s1;for( string::iterator i = s.begin();i != s.end();i++ ){if( *i != ' ' ){if( !state ){left = i;state = ON;}}else if( *i == ' ' ){if( state ){right = i;s1 += reverse( left,right ) + ' ';state = OFF;}}}if( s[s.size() - 1] != ' ')    s1 += reverse( left,s.end() );if( s1[s1.size() - 1] == ' ')    s1.erase( s1.end() - 1 );s = s1;}string reverse( string::iterator left,string::iterator right ){char c;for( string::iterator it1 = left,it2 = right - 1;it1 < it2;it1++,it2-- ){c = *it1;*it1 = *it2;*it2 = c;}string str( left,right );return str;}};