https://leetcode-cn.com/problems/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 <= 10^4
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?
class Solution {
public:
string reverseWords(string s) {
string tmp,ans;
vector<string> words;
s.push_back(' ');
for(char ch:s){
if (ch!=' ') tmp.push_back(ch);
else{
if (!tmp.empty()){
words.emplace_back(tmp);
tmp.clear();
}
}
}
reverse(words.begin(), words.end());
for(string w:words){
ans.push_back(' ');
ans.append(w);
}
return ans.substr(1);
}
};