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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

分析：

对一个字符串中得单词进行翻转，首先必须从字符串中分解出单词，然后将每个词压入堆栈，再依次弹出即可。

代码如下，运行时间约39ms：

class Solution {public:void reverseWords(string &s) {		string result;		int j = 0;		stack
   
     str_stack;		const char* pHead = s.c_str();		bool wordStart = false;		const char* pStr, *pBegin, *pEnd;		for (pStr=pHead; *pStr!='\0'; pStr++)		{
   

			if (!isspace(*pStr) && wordStart==false)

{				wordStart = true;				pBegin = pStr;				continue;			}			if (isspace(*pStr) && wordStart == true)			{				wordStart = false;				pEnd = pStr;				str_stack.push(s.substr(pBegin-pHead, pEnd-pBegin));			}		}		if (wordStart == true)		{			wordStart = false;			pEnd = pStr;			str_stack.push(s.substr(pBegin-pHead, pEnd-pBegin));		}		s.clear();		if (str_stack.size() > 0)		{						char space = ' ';			while (!str_stack.empty())			{				string stmp = str_stack.top();				str_stack.pop();			if (s.length() != 0)				{					s.push_back(space);				}				s = s + stmp;			}		}	}};

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