LeetCode 21. 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.

/** * 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* result;        if (l1->val < l2->val) {            result = l1;            l1 = l1->next;        }        else {            result = l2;            l2 = l2->next;        }        ListNode* cur = result;        while ((l1 != NULL) && (l2 != NULL)) {            if (l1->val < l2->val) {                cur->next = l1;                l1 = l1->next;            }            else {                cur->next = l2;                l2 = l2->next;            }            cur = cur->next;        }        if (l1 != NULL) {            cur->next = l1;        }        else {            cur->next = l2;        }        return result;    }};