【Leetcode】Reverse Words in a String

class Solution 
{
    vector<string> vs;
public:
    void reverseWords(string &s) 
    {
        string tmp;
        if(s == "")
            return;
        int start = 0;
        while(s[start] == ‘ ‘)
            start++;
        int end = s.length() - 1;
        while(s[end] == ‘ ‘)
            end--;
        if(start > end)
        {
            s = "";
            return;
        }
        for(int i = start;i <= end;i++)
        {
            if(s[i] == ‘ ‘)
            {
                vs.push_back(tmp);
                tmp.clear();
                while(s[i+1] == ‘ ‘)
                {
                    i++;
                }
            }
            else
            {
                tmp.push_back(s[i]);
            }
            
        }
        if(tmp == "")
            ;
        else
            vs.push_back(tmp);
        s = "";
        for(int i = vs.size() - 1;i > 0;i--)
        {
            s += vs[i];
            s += ‘ ‘;
        }
        s += vs[0];
    }
};

class Solution {
public:
    void reverseWords(string &s) {
        int start = 0;
        //skip beginning space
        while(start < s.length() && s[start] == ‘ ‘) 
            start++;
        int send = s.length() - 1;
        //skip end space
        while(send >= 0 && s[send] == ‘ ‘)
            send--;
        //change string s
        if(start > send) {
            s = "";
            return;
        }
        else
            s = s.substr(start,send-start+1);
        
        vector<string> words;
        //change mid space to one space
        int wordbegin = 0;
        for(int i = 0;i < s.length();i++) {
            if(s[i] == ‘ ‘) {
                words.push_back( s.substr(wordbegin,i-wordbegin) );
                while(i < s.length() && s[i] == ‘ ‘)
                    i++;
                wordbegin = i;
            }
            if(i == s.length() - 1) {
                words.push_back( s.substr(wordbegin,i-wordbegin+1) );
            }
        }
        //combination
        s = "";
        for(int i = words.size() - 1;i >= 0;i--) {
            if(i == 0) 
                s += words[i];
            else {
                s += words[i];
                s += " ";
            }
        }
    }
};