Leetcode 151：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".

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<string> str_stack;
		const char* pHead = s.c_str();
		bool wordStart = false;
		const char* pStr, *pBegin, *pEnd;
		for (pStr=pHead; *pStr!='\0'; pStr++)
		{

<span style="white-space: pre;">			</span>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;
			}
		}


	}
};