[C语言][LeetCode][21]Merge Two Sorted Lists

题目

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.

标签

Linked List

难度

简单

分析

题目意思是合并两个排好序的链表，并返回新的链表。解题思路是先找到链表的头，如果L1的第一个元素比较小，新链表的头结点就指向L1，如果L2的第一个元素比较小，新链表的头结点就指向L2。剩下的就是逐个比较剩余L1和L2里的元素。需要注意的是，最后是否比较结束了。

C代码实现

   struct ListNode *head;
    struct ListNode *ret;

    if(!l1 && l2)
        return l2;
    if(l1&&!l2)
        return l1;
    if(!l1 && !l2)
        return NULL;

    if(l1->val <= l2->val)
    {
        head = l1;
        l1 = l1->next;
    }
    else
    {
        head = l2;
        l2 = l2->next;
    }

    ret = head;

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

        head->next->next = NULL;
        head = head->next;        
    }

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

    return ret;