Merge Two Sorted Lists

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2){
struct ListNode dummy;
    struct ListNode* current = &dummy;

    while (list1 && list2) {
        if (list1->val <= list2->val) {
            current->next = list1;
            list1 = list1->next;
        } else {
            current->next = list2;
            list2 = list2->next;
        }
        current = current->next;
    }

    current->next = list1 ? list1 : list2;

    return dummy.next;
}