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&&l2==NULL)           return NULL;        if(l1==NULL)           return l2;        if(l2==NULL)           return l1;                ListNode* head = NULL;                if(l1->val>l2->val)          {              head = l2;              l2 = l2->next;          }          else          {              head = l1;              l1 = l1->next;          }        ListNode* node = head;        while(l1!=NULL&&l2!=NULL)        {           if(l1->val>l2->val)          {              node->next= l2;              l2 = l2->next;              node = node->next;          }          else          {              node->next = l1;              l1 = l1->next;              node = node->next;          }                       }        if(l1!=NULL)        {            node->next=l1;        }        if(l2!=NULL)        {            node->next=l2;        }        return head;    }};