leetCode(34):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.

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.

字符串反转的问题，有很多种方法。但本题要求删除多余的空格，所以比较特别，最直接的方法就是把所有单词取出来放到栈当中，再弹出。但题目要求不能用多余的辅助空间，所以只能在翻的时候去掉多余的空格。

class Solution {
public:
    void reverseWords(string &s) {
        reverse(s.begin(),s.end());

//首先去除头尾的空格
    	while(*(s.begin())==' ')
    	{
    		s.erase(s.begin());
    	}

    	while(*(s.end()-1)==' ')
    	{
    		s.erase(s.end()-1);
    	}
    	string::iterator iter1=s.begin();
    	string::iterator iter2=s.begin();

    	for(;iter2!=s.end();++iter2)
    	{
    		if(*iter2==' ' && *iter1!=' ')
    		{//反转每一个单词
    			reverse(iter1,iter2);
    			iter1=iter2+1;
    		}
    		else if(*iter2==' ' && *iter1==' ')
    		{//去除中间的空格
    			iter1--;
    			s.erase(iter2);
    			iter2=iter1;
    			iter1++;
    		}
    	}
    	reverse(iter1,s.end());//最后一个单词
    }
};

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