链接：https://leetcode.com/problems/reverse-words-in-a-string/description/

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

Example:  

Input: "the sky is blue",
Output: "blue is sky the".

Note:

• A word is defined as a sequence of non-space characters.
• Input string may contain leading or trailing spaces. However, your reversed string should not contain leading or trailing spaces.
• You need to reduce multiple spaces between two words to a single space in the reversed string.

Follow up: For C programmers, try to solve it in-place in O(1) space.

class Solution {
public:

    // function to reverse any part of string from i to j (just one word or entire string)
    void reverseword(string &s, int i, int j){
        while(i<j){
          char t=s[i];
          s[i++]=s[j];
          s[j--]=t;
        } 
    }
    
    void reverseWords(string &s) {
        
        int i=0, j=0;
        int l=0;
        int len=s.length();
        int wordcount=0;
        
        while(true){
            while(i<len && s[i] == ' ') i++;  // skip spaces in front of the word
            if(i==len) break;
            if(wordcount) s[j++]=' ';
            l=j;
            while(i<len && s[i] != ' ') {s[j++]=s[i++];} 
            reverseword(s,l,j-1);                // reverse word in place
            wordcount++;
            
        }
        
        s.resize(j);                           // resize result string
        reverseword(s,0,j-1);                  // reverse whole string
    }
};