go: add «2807. Insert Greatest Common Divisors in Linked List»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/insert-greatest-common-divisors-in-linked-list.go

@@ -0,0 +1,29 @@
+package main
+
+func insertGreatestCommonDivisors(head *ListNode) *ListNode {
+	gcd := func(x, y int) int {
+		for y != 0 {
+			x, y = y, x%y
+		}
+		return x
+	}
+	emplace := func(n *ListNode) *ListNode {
+		if n.Next == nil {
+			return n.Next
+		}
+
+		mid := ListNode{
+			Val:  gcd(n.Val, n.Next.Val),
+			Next: n.Next,
+		}
+		n.Next = &mid
+
+		return n.Next.Next
+	}
+
+	for node := head; node != nil; {
+		node = emplace(node)
+	}
+
+	return head
+}