【leetcode】151. Reverse Words in a String

题目：

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Update (2015-02-12):
For C programmers: Try to solve it in-place in O(1) space.

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.

c++代码：

class Solution {public:    void reverseOneWord(string &s, int start, int end){        while(start<end){            swap(s[start++],s[end--]);        }    }    void reverseWords(string &s) {        int i=0;  //快        int j=0;  //慢        int len=s.size();        int word_count=0;        while(i<len){            while(i<len && s[i]== ' '){  //找到下一个不为空的字符串                i++;            }//while            if(i>=len){                break;            }            if(word_count>0){  //如果不是第一个单词，那么每个单词前都需要加一个空格                s[j++]=' ';            }            int start=j;            for(;i<len && s[i]!=' ';i++,j++){  //从i开始的单词，移动到从j开始                s[j]=s[i];            }            reverseOneWord(s, start, j-1);  //翻转当前单词            word_count++;        }//while        s.resize(j);  //去掉最后一个单词后面的空字符串        reverseOneWord(s, 0, j-1);  //翻转整个单词    }};