# LeetCode - 0021. Merge Two Sorted Lists
### 題目網址：https://leetcode.com/problems/merge-two-sorted-lists/
###### tags: `LeetCode` `Easy` `連結串列（Linked List）`

/*
    -LeetCode format-
    Problem: 21. Merge Two Sorted Lists
    Difficulty: Easy
    
    by Inversionpeter
*/



/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if (!l1)
            return l2;
        if (!l2)
            return l1;
        ListNode *head, *now;
        if (l1->val < l2->val)
            head = l1, l1 = l1->next;
        else
            head = l2, l2 = l2->next;
        now = head;
        while (l1 || l2) {
            if (!l1) {
                now->next = l2;
                break;
            }
            else if (!l2) {
                now->next = l1;
                break;
            }
            else if (l1->val < l2->val) {
                now = now->next = l1, l1 = l1->next;
            }
            else {
                now = now->next = l2, l2 = l2->next;
            }
        }
        return head;
    }
};