[Leetcode 151, Medium] Reverse Words in a String

Problem:

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.

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.

Analysis:

Solutions:

C++:

    void reverseWords(string &s) 
    {
        for(int i = 0; i < s.size();) {
            if(s[i] != ' ')
                break;
                
            s.erase(s.begin());
        }
        
        if(s.empty())
            return;
            
        while(*(s.end() - 1) == ' ')
            s.erase(s.end() - 1);
        
        for(int i = 0; i < s.size();) {
            int j = i;
            for(; j < s.size() && s[j] != ' '; ++j) {}
            
            for(int start = i, end = --j; start < end;)
                swap(s[start++], s[end--]);

            while(j < s.size() - 2 && *(s.begin() + j + 2) == ' ')
                s.erase(s.begin() + j + 2);
                
            i = j + 2;
        }
        
        for(int start = 0, end = s.size() - 1; start < end;)
            swap(s[start++], s[end--]);
    }

Java:

Python: