# Merge Two Sorted Lists solution using TypeScript

Below is my TypeScript solution to the LeetCode "Merge Two Sorted Lists" question using a recursive approach.

Time Complexity: Because each node in each of the linked lists will be visited one time, the time complexity is O(m + n), where m represents the number of nodes in the first linked list and n represents the number of nodes in the second linked list.

Space Complexity: This approach will place m + n function calls on the stack, making the space complexity O(m + n).

``````/**
* class ListNode {
*     val: number
*     next: ListNode | null
*     constructor(val?: number, next?: ListNode | null) {
*         this.val = (val===undefined ? 0 : val)
*         this.next = (next===undefined ? null : next)
*     }
* }
*/

/**
* Merge two sorted linked lists and return it as a new sorted list.
*
*   Time Complexity: O(m + n)
*   Space Complexity: O(m + n)
*
*   Input: 1->2->4, 1->3->4
*   Output: 1->1->2->3->4->4
*/
function mergeTwoLists(l1: ListNode | null, l2: ListNode | null): ListNode | null {
if (l1 === null) {
return l2;
}
else if (l2 === null) {
return l1;
}
else if (l1.val < l2.val) {
l1.next = mergeTwoLists(l1.next, l2);
return l1;
} else {
l2.next = mergeTwoLists(l1, l2.next);
return l2
}
}
``````