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".

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.

class Solution {
private:
    void reviseString(string &s)
    {
        char *pCur  = &s.at(0);
        char *pCopy = pCur;
        
        while (*pCur != '\0')
        {
            while (*pCur != '\0' && *pCur == ' ' )
            {
                pCur++;    
            }
            
            if (*pCur == '\0')
            {
                *pCopy = '\0';
                break;
            }
            
            while (*pCur != '\0' && *pCur != ' ')
            {
                *pCopy++ = *pCur++;
            }
            
            if (*pCur == '\0')
            {
                *pCopy = '\0';
                break;
            }
            
            *pCopy++ = ' ';
            pCur++;
        }
        
        if ( (pCopy != &s.at(0)) && (*(pCopy-1) == ' '))
            *(pCopy-1) = '\0';
    
        return;
    
    }


    void reverseInternal(char *begin, char *end)
    {
        while (end > begin)
        {
            char temp = *end;
            *end = *begin;
            *begin = temp;
            
            end--;
            begin++;
        }
    }
    
public:
    void reverseWords(string &s) {
    
        if (s.size() == 0)
            return;   
       
        reviseString(s);
       
        if (s.size() == 0)
            return;
       
        char *pBegin = &s.at(0);
        char *pEnd   = pBegin+s.size()-1;
        
        // reverse the whole string
        reverseInternal(pBegin, pEnd);
        
        pBegin = pEnd = &s.at(0);

        // reverse each word
        while (*pEnd != '\0')
        {
            while(*pEnd != ' ' && *pEnd != '\0')
            {
                pEnd++;
            }
            
            char *pTemEnd = pEnd-1;
            reverseInternal(pBegin, pTemEnd);
            
            if (*pEnd == '\0')
                return;

            pBegin = ++pEnd;
        }            
    }
};