合并两个有序链表

将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

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

struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2){
    struct ListNode *Head = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode *prev = Head;
    

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

    prev->next = l1 != NULL ? l1 : l2;

    return Head->next;
}