LeetCode: 21. Merge Two Sorted Lists

 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.

 /**

 * 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 temp = new ListNode(0);

        ListNode current = temp;

        while (list1 != null && list2 != null){

            if (list1.val < list2.val) {

                current.next = list1;

                list1 = list1.next;

            }

            else  {

                current.next = list2;

                list2 = list2.next;

            }

            current = current.next;

        }

        if (list1 != null) {

            current.next = list1;

            list1 = list1.next;

        }

        if (list2 != null) {

            current.next = list2;

            list2 = list2.next;

        }

        return temp.next;

    }

}