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".

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.

思路：从头往后扫描字符串，从第一个开始不是空格算起。将单词放入temp中，直到遇到空格，作如下处理，将单词放入result中去，接下来再有单词可以放到上一个单词的前面，另加空格。如此反复，就可以将单词与单词为单位反转了。

class Solution {
public:
    void reverseWords(string &s) {
        int nLen=s.size();
        if(nLen<=0)
            return;
        string temp,result;
        int index=0;
        while(s[index]==' ')
            index++;
        for(int i=index;i<nLen;)
        {
            if(s[i]!=' ')
            {
                temp+=s[i];
                i++;
            }
            else
            {
                while(s[i]==' ')
                    i++;
                if(i==nLen)
                    break;
                result=" "+temp+result;
                temp="";
            }
        }
        s=temp+result;
    }
};