合并有序链表

Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.

Return the head of the merged linked list

func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
    head := &ListNode{}
    cur := head
    for l1 != nil || l2 != nil {
        if l1 != nil && l2 != nil {
            if l1.Val < l2.Val {
                cur.Next = l1
                l1 = l1.Next
            } else {
                cur.Next = l2
                l2 = l2.Next
            }
            cur = cur.Next
        } else if l1 != nil {
            cur.Next = l1
            break
        } else {
            cur.Next = l2
            break
        }
    }
    return head.Next
}