【数据结构】【链表代码】合并有序链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
 typedef struct ListNode Node;
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
    if(l1==NULL)
        return l2;
    if(l2==NULL)
        return l1;   
    //取小的尾插
    Node*head=NULL,*tail=NULL;
    if(l1->val<l2->val){
        head=tail=l1;
        l1=l1->next;
    }else{
        head=tail=l2;
        l2=l2->next;

    }

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

    if(l1)
        tail->next=l1;
    else
        tail->next=l2;
    return head;
}