(leetcode 1)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.

void reverseWords(string &s) {
        if(s=="")
        return;
    int i = s.size()-1,flagL,flagR;
    string tmp = "";
    for(; i >= 0; i--)
    {
        while(i >= 0 && ' '== s[i])i--;
        flagR = i; //从右开始找到第一个不是 “  ” 的字符位置
        while(i >= 0 && ' '!= s[i])i--;
        flagL = i+1;//从右向左开始找到第二个不是 “  ” 的字符位置
        if(flagL>=0&&flagR>=0)
            tmp += s.substr(flagL,flagR-flagL+1)+" ";
    }
        s = tmp;
        if(s.size()>1)
            s.erase(s.size()-1,1);
    }