leetcode【151】【tag String】Reverse Words in a String【c++版本，多種解法，翻轉法和巧妙字符串流】

問題描述：

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

Example 1:

Input: "the sky is blue"
Output: "blue is sky the"

Example 2:

Input: "  hello world!  "
Output: "world! hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: "a good   example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

源碼：

問題意思大概就是翻轉句子，並且把多個空格變成一個

這題和劍指offer第二版的58題很像。詳情可以看劍指offer總綱。不過需要多餘考慮的是多個空格爲問題。

思路就是先整個翻轉，然後對每個單詞依次翻轉，中間多考慮一下多空格問題。比如

I LOVE YOU->UOY EVOL I->YOU LOVE I

源碼如下：

class Solution {
public:
    string reverseWords(string s) {
        int n = s.length(), index = 0;
        reverse(s.begin(), s.end());
        for(int i=0; i<n; i++){
            if(s[i] != ' '){
                if(index != 0)      s[index++] = ' ';
                int j=i;
                while(j<n && s[j]!=' ')     s[index++] = s[j++];
                reverse(s.begin()+index-(j-i), s.begin()+index);
                i = j;
            }
        }
        s.resize(index);
        return s;
    }
};

在網上查了一下，有大佬用字符流的方法做的，很巧妙：

第一種：

class Solution {
public:
    string reverseWords(string s) {
        istringstream is(s);
        string tmp;
        is >> s;
        while(is >> tmp) s = tmp + " " + s;
        if(!s.empty() && s[0] == ' ') s = "";
        return s;
    }
};

第二種：

class Solution {
public:
    string reverseWords(string s) {
        istringstream is(s);
        s = "";
        string t = "";
        while (getline(is, t, ' ')) {
            if (t.empty()) continue;
            s = (s.empty() ? t : (t + " " + s));
        }
        return s;
    }
};