合并两个有序链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */


struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2)
{
    if(l1==NULL)
    {
        return l2;
    }
    if(l2==NULL)
    {
        return l1;
    }
    struct ListNode* head = malloc(sizeof(struct ListNode));
    head->val = 0;
    head->next = NULL;
    struct ListNode* t = head;
    while(l1!=NULL && l2!=NULL)
    {
        if(l1->val > l2->val)
        {
            t->next =l2;
            l2 = l2->next;
            t=t->next;
        }
        else
        {
            t->next = l1;
            l1 = l1->next;
            t=t->next;
        }
    }
    if(l2==NULL)
    {
        t->next=l1;
    }
    else
    {
        t->next=l2;
    }
    return head->next;
}