/**
 * 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}
 */

// Time Complexity: O(m + n)
// Space Complexity: O(m + n)  

var mergeTwoLists = function(list1, list2) {

    
    if(!(list1 && list2)) {
        return list1 || list2;
    }

    if(list1.val < list2.val) {
        list1.next = mergeTwoLists(list1.next, list2);
        return list1;
    } else {
        list2.next = mergeTwoLists(list1, list2.next);
        return list2;
    }
    
};


