leetcode-patterns-java/LeetCode_Problems/Java/easy/0021. Merge Two Sorted Lists.java at main · elchibek5/leetcode-patterns-java · GitHub

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode dummy = new ListNode();
        ListNode tail = dummy;

        while (list1 != null && list2 != null) {
            if (list1.val < list2.val) {
                tail.next = list1;
                list1 = list1.next;
            } else {
                tail.next = list2;
                list2 = list2.next;
            }
            tail = tail.next;
        }
        if (list1 != null) {
            tail.next = list1;
        } else {
            tail.next = list2;
        }
        return dummy.next;
    }
}
// SOLUTION 2
// /**
//  * Definition for singly-linked list.
//  * public class ListNode {
//  *     int val;
//  *     ListNode next;
//  *     ListNode() {}
//  *     ListNode(int val) { this.val = val; }
//  *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
//  * }
//  */
// class Solution {
//     public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
//         return mergeLinkedList(list1, list2);
//     }

//     private ListNode mergeLinkedList(ListNode l1, ListNode l2) {
//         if (l1 == null) {
//             return l2;
//         }
//         if (l2 == null) {
//             return l1;
//         }

//         if (l1.val <= l2.val) {
//             l1.next = mergeLinkedList(l1.next, l2);
//             return l1;
//         } else {
//             l2.next = mergeLinkedList(l1, l2.next);
//             return l2;
//         }
//     }
// }