Merge Two Sorted Lists

struct ListNode { int val; ListNode* next; };

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* a, ListNode* b) {
        ListNode dummy{0, nullptr};
        ListNode* tail = &dummy;
        while (a && b) {
            if (a->val <= b->val) { tail->next = a; a = a->next; }
            else { tail->next = b; b = b->next; }
            tail = tail->next;
        }
        tail->next = a ? a : b;
        return dummy.next;
    }
};

func mergeTwoLists(a *ListNode, b *ListNode) *ListNode {
    dummy := &ListNode{}
    tail := dummy
    for a != nil && b != nil {
        if a.Val <= b.Val {
            tail.Next = a
            a = a.Next
        } else {
            tail.Next = b
            b = b.Next
        }
        tail = tail.Next
    }
    if a != nil {
        tail.Next = a
    } else {
        tail.Next = b
    }
    return dummy.Next
}

from typing import Optional

class Solution:
    def mergeTwoLists(
        self,
        a: Optional[ListNode],
        b: Optional[ListNode],
    ) -> Optional[ListNode]:
        dummy = ListNode()
        tail = dummy
        while a and b:
            if a.val <= b.val:
                tail.next = a
                a = a.next
            else:
                tail.next = b
                b = b.next
            tail = tail.next
        tail.next = a if a else b
        return dummy.next

function mergeTwoLists(a, b) {
    const dummy = new ListNode(0);
    let tail = dummy;
    while (a && b) {
        if (a.val <= b.val) {
            tail.next = a;
            a = a.next;
        } else {
            tail.next = b;
            b = b.next;
        }
        tail = tail.next;
    }
    tail.next = a ? a : b;
    return dummy.next;
}

class Solution {
    public ListNode mergeTwoLists(ListNode a, ListNode b) {
        ListNode dummy = new ListNode(0);
        ListNode tail = dummy;
        while (a != null && b != null) {
            if (a.val <= b.val) {
                tail.next = a;
                a = a.next;
            } else {
                tail.next = b;
                b = b.next;
            }
            tail = tail.next;
        }
        tail.next = (a != null) ? a : b;
        return dummy.next;
    }
}

function mergeTwoLists(a: ListNode | null, b: ListNode | null): ListNode | null {
    const dummy = new ListNode(0);
    let tail: ListNode = dummy;
    while (a && b) {
        if (a.val <= b.val) {
            tail.next = a;
            a = a.next;
        } else {
            tail.next = b;
            b = b.next;
        }
        tail = tail.next as ListNode;
    }
    tail.next = a ? a : b;
    return dummy.next;
}