Merge pull request #3394 from drxlx/2130-maximum-twin-sum-of-a-linked…

…-list

swift/2130-maximum-twin-sum-of-a-linked-list.swift

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+/**
+ * Question Link: https://leetcode.com/problems/maximum-twin-sum-of-a-linked-list/
+ */
+
+ /**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public var val: Int
+ *     public var next: ListNode?
+ *     public init() { self.val = 0; self.next = nil; }
+ *     public init(_ val: Int) { self.val = val; self.next = nil; }
+ *     public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
+ * }
+ */
+class Solution {
+    func pairSum(_ head: ListNode?) -> Int {
+        var slow = head
+        var fast = head
+        var prev: ListNode?
+        while fast != nil && fast?.next != nil {
+            fast = fast?.next?.next
+            var tmp = slow?.next
+            slow?.next = prev
+            prev = slow
+            slow = tmp
+        }
+        var res = 0
+        while slow != nil {
+            res = max(res, prev!.val + slow!.val)
+            prev = prev?.next
+            slow = slow?.next
+        }
+        return res
+    }
+}