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.
Example 4:
Input: s = " Bob Loves Alice "
Output: "Alice Loves Bob"
Example 5:
Input: s = "Alice does not even like bob"
Output: "bob like even not does Alice"
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?
class Solution {
public String reverseWords(String s) {
Stack<String> stack = new Stack<>();
String temp = "";
for(int i=0;i<s.length();i++){
if(s.charAt(i)==' '&&temp.length()!=0){
stack.push(temp);
temp = "";
}else if(s.charAt(i)!=' '){
temp += s.charAt(i);
}
if(i==s.length()-1){
stack.push(temp.trim());
}
}
String result = "";
while(!stack.isEmpty()){
result += stack.pop();
result += " ";
}
return result.strip();
}
}