Create 0234-palindrome-linked-list.kt

kotlin/0234-palindrome-linked-list.kt

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+/**
+ * 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 isPalindrome(head: ListNode?): Boolean {
+
+ var slow = head
+ var fast = head
+
+ // find the middle
+ while(fast != null && fast.next != null) {
+ fast = fast?.next?.next
+ slow = slow?.next
+ }
+
+ //reverse the right part of list (from middle to end)
+ var prev: ListNode? = null
+ while(slow != null) {
+ val temp = slow?.next
+ slow?.next = prev
+ prev = slow
+ slow = temp
+ }
+
+ //traverse both divided parts, left and right portion, to check if palindrome
+ var left = head
+ var right = prev
+ while(right != null) {
+ if(right?.`val` != left?.`val`) return false
+ left = left?.next
+ right = right?.next
+ }
+
+ return true
+ }
+}