[leetcode]557. Reverse Words in a String III

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.

Note: In the string, each word is separated by single space and there will not be any extra space in the string.

Example 1:

Input: "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"

分析：

反转字符串中的每个单词，保持一开始的单词和空格顺序，其中不会有多余空格。可以用两个指针，分别指向每个单词的开头和结尾位置，再用两个指针对单词进行首尾交换即可。

class Solution {
public:
    string reverseWords(string s) {
        int start = 0, end = 0, n = s.size();
        while (start < n && end < n) {
            while (end < n && s[end] != ' ') 
                ++end;
            for (int i = start, j = end - 1; i < j; ++i, --j) 
            {
                swap(s[i], s[j]);
            }
            start = ++end;
        }
        return s;
    }
};