Create 0234-palindrome-linked-list.kt

Author: a93a

kotlin/0234-palindrome-linked-list.kt

@@ -0,0 +1,42 @@
+/**
+ * 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
+    }
+}