一、题目

151. Reverse Words in a String

Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

Example 1:

Input: s = “the sky is blue”
Output: “blue is sky the”
Example 2:

Input: s = " hello world "
Output: “world hello”
Explanation: Your reversed string should not contain leading or trailing spaces.
Example 3:

Input: s = “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.

Constraints:

1 <= s.length <= 104
s contains English letters (upper-case and lower-case), digits, and spaces ’ '.
There is at least one word in s.

Follow-up: If the string data type is mutable in your language, can you solve it in-place with O(1) extra space?

二、题解

class Solution {
public:string reverseWords(string s) {vector<string> tmp;istringstream ss(s);string token;while(getline(ss,token,' ')) tmp.push_back(token);string res = "";int n = tmp.size();for(int i = n - 1;i >= 0;i--){if(tmp[i] != ""){res += tmp[i];res += " ";}}//去除末尾空格while(res.back() == ' ') res.pop_back();return res;}
};