leetcode【151】【tag String】Reverse Words in a String【c++版本，多种解法，翻转法和巧妙字符串流】

问题描述：

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.

源码：

问题意思大概就是翻转句子，并且把多个空格变成一个

这题和剑指offer第二版的58题很像。详情可以看剑指offer总纲。不过需要多余考虑的是多个空格为问题。

思路就是先整个翻转，然后对每个单词依次翻转，中间多考虑一下多空格问题。比如

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

源码如下：

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;
    }
};

在网上查了一下，有大佬用字符流的方法做的，很巧妙：

第一种：

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;
    }
};

第二种：

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;
    }
};