[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.

想法很朴素：

1.将单词分出来。

2.类似头插法，将单词插入到新的字符串，就能反过来了。

    void reverseWords(string &s)
    {
        if (s == "")return;
        int i = 0;
        string temp="";
        string temp2 = "";         
        while (s[i]!='')
        {
            if (s[i] != ' ')
            {
                temp.append(s.substr(i, 1));
                i++;
            }
            else//空格
            {
                if (temp != "")
                {
                    temp2.insert(0, " ");
                    temp2.insert(0, temp);
                    temp.clear();
                }                
                i++;             
            }
        }
        temp2.insert(0, " ");
        temp2.insert(0, temp);
        
        cout << temp2.c_str() << endl;
        temp2.erase(temp2.size()-1, 1);//擦去最后一个空格
        cout << temp2.c_str() << endl;
        
        s.clear();
        s = temp2;
        i = s.size() - 1;
        while (s[i] == ' ')//擦除结尾空格
        {
            s.erase(i, 1);
            i = s.size() - 1;
        }
        i = 0;
         while (s[i] == ' ')//擦除前面空格
         {
             s.erase(i, 1);             
         }
    }