Solution.go

/**
 * Definition for a Node.
 * type Node struct {
 *     Val int
 *     Next *Node
 *     Random *Node
 * }
 */

 func copyRandomList(head *Node) *Node {
    if head == nil {
        return nil
    }

    cur := head
    for cur != nil {
        node := &Node{
            Val: cur.Val,
            Next: cur.Next,
            Random: nil,
        }
        cur.Next = node
        cur = node.Next
    }

    cur = head
    for cur != nil {
        if cur.Random == nil {
            cur.Next.Random = nil
        } else {
            cur.Next.Random = cur.Random.Next
        }
        cur = cur.Next.Next
    }

    copy := head.Next
    cur = head
    for cur != nil {
        next := cur.Next
        cur.Next = next.Next
        if (next.Next == nil) {
            next.Next = nil
        } else {
            next.Next = next.Next.Next
        }
        cur = cur.Next
    }
    return copy
}