[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

".

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) {
        stringstream str(s);
        string word, res;
        stack<string> stk;
        while(str >> word)
            stk.push(word);
        if(!stk.empty())
        {
            res = stk.top();
            stk.pop();
        }
        while(!stk.empty())
        {
            res += " ";
            res += stk.top();
            stk.pop();
        }
        s = res;
    }
};

上面是我自己的方法，用了stringstream这个流，头文件是<sstream>，搜了下别人的方法，也非常巧妙。

class Solution {
public:
    void reverseWords(string &s) {
        string res;
        for(int i = s.length() - 1; i >= 0; i--)
        {
            while(i >= 0 && s[i] == ' ') i--;
            if(i < 0)   break;
            if(!res.empty())
                res += " ";
            string t;
            while(i >= 0 && s[i] != ' ')
                t += s[i--];
            reverse(t.begin(), t.end());
            res += t;
        }
        s = res;
    }
};