[LeetCode] 21. Merge Two Sorted Lists

[Animenzzzz]

Description

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.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

解题思路：这题和 23题：合并K个链表类似，是其子处理，注意细节就好

C解法：

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