solved: 2

Author: ryoppippi

code/2.add-two-numbers.ts

@@ -0,0 +1,37 @@
+/**
+ * Definition for singly-linked list.
+ * 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)
+ *     }
+ * }
+ */
+
+function addTwoNumbers(
+  l1: ListNode | null,
+  l2: ListNode | null,
+  carry: number = 0,
+): ListNode | null {
+  if (!l1 && !l2 && carry === 0) {
+    return null;
+  }
+
+  const firstNum = l1 ? l1.val : 0;
+  const secondNum = l2 ? l2.val : 0;
+  const summation = firstNum + secondNum + carry;
+
+  carry = Math.floor(summation / 10);
+  const num = summation % 10;
+
+  const currentNode = new ListNode(num);
+  currentNode.next = addTwoNumbers(
+    l1 ? l1.next : null,
+    l2 ? l2.next : null,
+    carry,
+  );
+
+  return currentNode;
+}