From f910e9af9038b21d8785f332743d51b20ffffede Mon Sep 17 00:00:00 2001
From: Stormborn <kruglov.matvey@outlook.com>
Date: Sun, 13 Aug 2023 22:33:19 +0300
Subject: [PATCH] Create: 2130-maximum-twin-sum-of-a-linked-list.go

---
 go/2130-maximum-twin-sum-of-a-linked-list.go | 51 ++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 go/2130-maximum-twin-sum-of-a-linked-list.go

diff --git a/go/2130-maximum-twin-sum-of-a-linked-list.go b/go/2130-maximum-twin-sum-of-a-linked-list.go
new file mode 100644
index 000000000..c038d7512
--- /dev/null
+++ b/go/2130-maximum-twin-sum-of-a-linked-list.go
@@ -0,0 +1,51 @@
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func pairSum(head *ListNode) int {
+	// find mid of a list
+	slow := head
+	fast := head.Next
+	for fast != nil && fast.Next != nil {
+		slow = slow.Next
+		fast = fast.Next.Next
+	}
+
+	// reverse links in 2nd half
+	second := reverse(slow.Next)
+	// split into 2 lists
+	slow.Next = nil
+
+	// traverse two lists with pointers and compare twin sum
+	first := head
+	var maxSum int
+	for first != nil && second != nil {
+		maxSum = max(maxSum, first.Val+second.Val)
+		first = first.Next
+		second = second.Next
+	}
+	return maxSum
+}
+
+func reverse(node *ListNode) *ListNode {
+	var curr, prev *ListNode = node, nil
+	for curr != nil {
+		tmp := curr.Next
+		curr.Next = prev
+		prev = curr
+		curr = tmp
+	}
+	return prev
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+//Time: O(n)
+//Space: O(1)