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.

Solution

class Solution {

public String reverseWords(String s) {

// Remove leading and trailing spaces and then split the words with whitespace regex

String[] str = s.trim().split("\\s+");

StringBuilder sb = new StringBuilder();

// iterate the words in reverse order

for(int i=str.length-1; i>0; i--) {

// append current word and space to output

sb.append(str[i]).append(" ");

}

// append first word to output

sb.append(str[0]);

return sb.toString();

}

}