LeetCode151：Reverse Words in a String

題目：

Given an input string, reverse the string word by word.

For example,
     Given s = "the sky is blue",
     return "blue is sky the".

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.

實現程式碼：

#include <iostream>
#include <algorithm>
#include <stack>
#include <string>
#include <sstream>
using namespace std;

/*

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

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.
*/

class Solution {
public:
    void reverseWords(string &s) 
    {
        
        reverse(s.begin(), s.end());
        string::iterator p_iter = s.begin();
        string::iterator q_iter;
        
        //去除最前面和最後面的空白符
        int index = s.find_first_not_of(' ');
        if(index == string::npos)//如果字串全為空白符 
        {
            s.clear();
            return;
        }
        s.erase(s.begin(), s.begin()+index);
        int index2 = s.find_last_not_of(' ');
        s.erase(s.begin()+index2+1, s.end()); 
                        
        p_iter = s.begin();
        while(p_iter != s.end())
        {            
            q_iter = p_iter;
            while(*p_iter != ' ' && p_iter != s.end()) p_iter++;
            reverse(q_iter, p_iter);
            bool first = true;
            while(*p_iter == ' ' && p_iter != s.end())//去掉單詞間多個空白符，只留下一個 
            {
                if(first)
                {
                    p_iter++;
                    first = false;
                }                    
                else
                    p_iter = s.erase(p_iter);
            }

        }
    }

    
 
};

int main(void)
{
    string str = " this is   zhou ";
    Solution solution;
    solution.reverseWords(str);
    cout<<str<<endl;
    return 0;
}