Create: 2130-maximum-twin-sum-of-a-linked-list.go

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)