LeetCode in Kotlin
24. Swap Nodes in Pairs
Medium
Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)
Example 1:
Input: head = [1,2,3,4]
Output: [2,1,4,3]
Example 2:
Input: head = []
Output: []
Example 3:
Input: head = [1]
Output: [1]
Constraints:
- The number of nodes in the list is in the range
[0, 100]. 0 <= Node.val <= 100
Solution
import com_github_leetcode.ListNode
/*
* Example:
* var li = ListNode(5)
* var v = li.`val`
* Definition for singly-linked list.
* class ListNode(var `val`: Int) {
* var next: ListNode? = null
* }
*/
class Solution {
fun swapPairs(head: ListNode?): ListNode? {
if (head == null) {
return null
}
val len = getLength(head)
return reverse(head, len)
}
private fun getLength(currLocal: ListNode): Int {
var curr: ListNode? = currLocal
var cnt = 0
while (curr != null) {
cnt++
curr = curr.next
}
return cnt
}
// Recursive function to reverse in groups
private fun reverse(head: ListNode?, len: Int): ListNode? {
// base case
if (len < 2) {
return head
}
var curr = head
var prev: ListNode? = null
var next: ListNode?
for (i in 0..1) {
// reverse linked list code
next = curr!!.next
curr.next = prev
prev = curr
curr = next
}
head!!.next = reverse(curr, len - 2)
return prev
}
}