LeetCode in Kotlin
151. Reverse Words in a String
Medium
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 <= 104scontains 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?
Solution
class Solution {
fun reverseWords(s: String): String {
val sb = StringBuilder()
var i = s.length - 1
while (i >= 0) {
if (s[i] == ' ') {
i--
continue
}
val start = s.lastIndexOf(' ', i)
sb.append(' ')
sb.append(s, start + 1, i + 1)
i = start - 1
}
if (sb.length > 0) {
sb.deleteCharAt(0)
}
return sb.toString()
}
}