[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.

题目很简单，没啥好说的。

/** * 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) {        ListNode* ptr = new ListNode(0);        ListNode* l3 = ptr;        if (l1 == NULL)            return l2;        if (l2 == NULL)            return l1;        while (l1 != NULL && l2 != NULL)        {            if (l1->val <= l2->val)            {                l3->next = l1;                l1 = l1->next;            }            else            {                l3->next = l2;                l2 = l2->next;            }            l3 = l3->next;        }        while (l1)        {                l3->next = l1;                l1 = l1->next;                l3 = l3->next;        }        while (l2)        {                l3->next = l2;                l2 = l2->next;                l3 = l3->next;        }        l3 = ptr->next;        delete ptr;        return l3;    }};