Easy 6 Merge Two Sorted Lists（21）

Description
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
将两个有序链表合并成一个链表。（定义一个头结点，方便返回）

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} //初始化 * }; */class Solution {public:    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {        ListNode dummy(INT_MIN);        ListNode *tail = &dummy;        while (l1 && l2) {            if (l1->val < l2->val) {                tail->next = l1;                l1 = l1->next;            } else {                tail->next = l2;                l2 = l2->next;            }            tail = tail->next;        }        tail->next = l1 ? l1 : l2;        return dummy.next;    }};