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 {
public:
    void reverseWords(string &s) {
        // Skip the spaces on the left
        int pos = 0;
        for(; pos < s.length(); pos ++) {
            if(s[pos] != ' ')
                break;
        }

        string result;
        string word;
        for(; pos < s.length(); pos ++) {
            // If is space, check if we have word. Have, record it. Not have, skip.
            if(s[pos] == ' ') {
                if(word.length() != 0) {
                    if(!result.empty())
                        result = " " + result;
                    result = word + result;
                    word.clear();
                }
            }
            else {
                word += s[pos];
            }
        }
        
        if(word != "") {
            if(!result.empty())
                result = " " + result;
            result = word + result;
        }
        
        if(result.length() != 0) {
            if(result[0] == ' ') {
                s = result.substr(1);
                return;
            }
        }
        s = result;
    }
};