LeetCode in Kotlin
541. Reverse String II
Easy
Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string.
If there are fewer than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and leave the other as original.
Example 1:
Input: s = “abcdefg”, k = 2
Output: “bacdfeg”
Example 2:
Input: s = “abcd”, k = 2
Output: “bacd”
Constraints:
1 <= s.length <= 104sconsists of only lowercase English letters.1 <= k <= 104
Solution
class Solution {
fun reverseStr(s: String, k: Int): String {
val res = StringBuilder()
var p1 = 0
var p2 = 2 * k - 1
if (s.length < k) {
res.append(reverse(s))
return res.toString()
}
while (p1 < s.length) {
if (s.length < p1 + k) {
res.append(reverse(s.substring(p1)))
} else {
res.append(reverse(s.substring(p1, p1 + k)))
if (s.length < p2 + 1) {
res.append(s.substring(p1 + k))
} else {
res.append(s, p1 + k, p2 + 1)
}
}
p1 = p1 + 2 * k
p2 = p2 + 2 * k
}
return res.toString()
}
private fun reverse(s: String): String {
val sb = StringBuilder()
sb.append(s)
sb.reverse()
return sb.toString()
}
}