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.

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.

解法简述：

    逐个取元素，第一个循环排除空格，第二个循环在遇到空格或null前将字幕出入缓存单元的第一个位置，这样在遇到空格时为一个正序的单词；

    再设定一个缓存string 每获得一个单词就拼接起来末尾加空格；

    最后拼接完后，因为排除空格的循环设在第一位，导致最后若存在多个空格时会存入多个空格，因此多设一层循环排除末尾多出空格。

代码如下：

class Solution {public:    void reverseWords(string &s) {        string rs,temp;        int i = s.length()-1;        while(s[i] != NULL){        while(s[i] == ' ' && s[i] != NULL) i--;        while(s[i] != ' ' && s[i] != NULL){        temp.insert(0,1,s[i]);        i--;}rs = rs + temp + " ";temp = "";i--;}rs = rs + temp;s = rs;i = s.length()-1;while(s[i] == ' '){s.erase(i ,1);i--;}    }};