C语言 合并2个有序链表

题目链接:

https://leetcode.cn/problems/merge-two-sorted-lists/description/?envType=study-plan-v2&envId=selected-coding-interview

参考题解。

https://leetcode.cn/problems/merge-two-sorted-lists/solutions/1734801/by-elegant-franklin6qn-mo0y/?envType=study-plan-v2&envId=selected-coding-interview

问题记录:

对于一个 struct 定义的结构体，如果使用指针了， 如何初始化一个实例？

struct ListNode {
   int val;
   struct ListNode *next;
 };

这个写法就不行！

struct ListNode *head = {NULL, NULL};

正确的写法是:

struct ListNode *head = (struct ListNode*)malloc(sizeof(struct ListNode));

完整代码

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


// 参考题解。
// https://leetcode.cn/problems/merge-two-sorted-lists/solutions/1734801/by-elegant-franklin6qn-mo0y/?envType=study-plan-v2&envId=selected-coding-interview

 
struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2) {
    // struct ListNode *head = {NULL, NULL};

    struct ListNode *head = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode *dummy = head;

    while (true) {
        if (!list1) {
            dummy->next = list2;
            break;
        }
        
        if (!list2) {
            dummy->next = list1;
            break;
        }

        if (list1->val < list2->val) {
            dummy->next = list1;
            list1 = list1->next;
        } else {
             dummy->next = list2;
            list2 = list2->next;
        }

        dummy = dummy->next;

    }
    return head->next;
}