Leetcode 557. Reverse Words in a String III

题目：Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.
Example 1:
Input: “Let’s take LeetCode contest”
Output: “s’teL ekat edoCteeL tsetnoc”
Note: In the string, each word is separated by single space and there will not be any extra space in the string.

面CVTE的实习的时候抽到了一道题跟这道题目类似，我抽到的题目是要把单词的位置对调，比如you are dog就变成dog are you.

这道题的代码如下：

class Solution {
public:
    string inv(string str){
        for(int i = 0; i < str.length()/2; i++)
        {
            char tmp;
            tmp = str[i];
            str[i] = str[str.length()-1-i];
            str[str.length()-1-i] = tmp;
        }
        return str;
    }
    string reverseWords(string s) {
        int begin = 0, end = 0;
        string res = "";
        while(end < s.length()){
            while(end != s.length()-1 && s[end] != ' '){
                end++;
            }
            if(end != s.length()-1)
                res += inv(s.substr(begin, end-begin)) + " ";
            else
                res += inv(s.substr(begin, end+1-begin));
            begin = end+1;
            end++;
        }
        return res;
    }
};