Create 2130-maximum-twin-sum-of-a-linked-list.kt

Author: a93a

kotlin/2130-maximum-twin-sum-of-a-linked-list.kt

@@ -0,0 +1,35 @@
+/**
+ * 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 pairSum(head: ListNode?): Int {
+        var slow = head
+        var fast = head
+        var prev: ListNode? = null
+
+        while(fast != null && fast.next != null) {
+            fast = fast.next.next
+            val temp = slow?.next
+            slow?.next = prev
+            prev = slow
+            slow = temp
+        }
+
+        var res = 0
+        while(slow != null && prev != null) { // only need to check if either one of these != null, I check both for null safety warnings
+            res = maxOf(res, slow.value!! + prev.value!!)
+            prev = prev.next
+            slow = slow.next
+        }
+
+        return res
+    }
+
+    val ListNode.value get()= this.`val`
+}