21. Merge Two Sorted Lists

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LeetCode

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Problem

You are given the heads of two sorted linked lists list1 and list2.

Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.

Return the head of the merged linked list.

Example 1:

Input: list1 = [1,2,4], list2 = [1,3,4]
Output: [1,1,2,3,4,4]

Example 2:

Input: list1 = [], list2 = []
Output: []

Example 3:

Input: list1 = [], list2 = [0]
Output: [0]

Constraints:

• The number of nodes in both lists is in the range [0, 50].
• -100 <= Node.val <= 100
• Both list1 and list2 are sorted in non-decreasing order.

Code

class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(-1);
        ListNode curr = dummy;

        while(l1 != null || l2 != null){
            int x = l1 == null ? Integer.MAX_VALUE : l1.val;
            int y = l2 == null ? Integer.MAX_VALUE : l2.val;

            if(x < y){
                curr.next = new ListNode(x);
                l1 = l1.next;
            } else {
                curr.next = new ListNode(y);
                l2 = l2.next;
            }

            curr = curr.next;
        }

        return dummy.next;
    }
}

class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(-1);
        ListNode curr = dummy;

        while(l1 != null && l2 != null){
            if(l1.val < l2.val) {
                curr.next = l1;
                l1 = l1.next;
            } else {
                curr.next = l2;
                l2 = l2.next;
            }

            curr = curr.next;
        }

        if(l1 != null) {
            curr.next = l1;
        }

        if(l2 != null) {
            curr.next = l2;
        }

        return dummy.next;
    }
}