Merge Two Sorted Lists

题目：

Merge two sorted (ascending) linked lists and return it as a new sorted list. The new sorted list should be made by splicing together the nodes of the two lists and sorted in ascending order.

分析：

基本题，没有什么特别想说的。

解法：

class Solution {
public:
    /**
     * @param ListNode l1 is the head of the linked list
     * @param ListNode l2 is the head of the linked list
     * @return: ListNode head of linked list
     */
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        // write your code here
        if (l1 == NULL) {
            return l2;
        }

        if (l2 == NULL) {
            return l1;
        }

        ListNode dummy(0);
        ListNode* curr = &dummy;

        while (l1 != NULL && l2 != NULL) {
            if (l1->val <= l2->val) {
                curr->next = l1;
                l1 = l1->next;
            } else {
                curr->next = l2;
                l2 = l2->next;
            }
            curr = curr->next;
        }

        if (l1 != NULL) {
            curr->next = l1;
        }

        if (l2 != NULL) {
            curr->next = l2;
        }

        return dummy.next;
    }
};