Leetcode -- 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".

Update (2015-02-12):
For C programmers: Try to solve it in-place in O(1) space.

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.

分析：

先去除多余的空格，再做两次reverse。

class Solution {
public:
    void reverseWords(string &s) {
        for(int i=0;i<s.size();)
    	{
    		if(s[i]==' '&&(i==0||i==s.size()-1||s[i+1]==' '))
    			s.erase(i,1);
    		else i++;
    	}
    	int n=s.size();
    	if(n==0) return;
    
    	reverse(s.begin(),s.end());
    	for(int i=0;i<s.size();)
    	{
    		int j=i+1;
    		while(j<n&&s[j]!=' ') j++;
    		reverse(next(s.begin(),i),next(s.begin(),j));
    		i=j+1;
    	}
    }
};