Leetcode 21 Merge Two Sorted Lists

题目要求：

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.

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建立一个新表头，遍历比较两个列表的节点值大小，将较小的加入新链表，最后在将没遍历结束的链表加到新链表尾部

代码如下：

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