LeetCode-Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Solution:

Code:

<span style="font-size:14px;">/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        if (l1 == NULL) return l2;
        if (l2 == NULL) return l1;
        ListNode *begin, *end;
        if (l1->val < l2->val) {
            begin = l1;
            end = l1;
            l1 = l1->next;
        } else {
            begin = l2;
            end = l2;
            l2 = l2->next;
        }
        while (l1 != NULL && l2 != NULL) {
            if (l1->val < l2->val) {
                end->next = l1;
                end = l1;
                l1 = l1->next;
            } else {
                end->next = l2;
                end = l2;
                l2 = l2->next;
            }
        }
        if (l1 != NULL) end->next = l1;
        else end->next = l2;
        return begin;
    }
};</span>