Merge Two Sorted Lists

Description

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.

Solution(javascript)

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} list1
 * @param {ListNode} list2
 * @return {ListNode}
 */
var mergeTwoLists = function(list1, list2) {
    let outputList = new ListNode();
    let selectedNode = outputList;
    let tempNode;
    while (true) {
        if (list1 && list2 && list1.val <= list2.val || list1 && list2 == undefined) {
            selectedNode.next = list1;
            list1 = list1.next;
        } else if (list1 && list2 || list2 && list1 == undefined) {
            selectedNode.next = list2;
            list2 = list2.next;
        } else {
            break;
        }
        selectedNode = selectedNode.next;
    }
    return outputList.next;
};