add exercise 0206

Author: charliesbot

typescript/0206_reverse_linked_list/0206_reverse_linked_list.test.ts

@@ -0,0 +1,26 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+
+const reverseList = function (head: ListNode): ListNode {
+  let node: ListNode | null = head;
+  let prevNode: ListNode | null = null;
+  let nextNode: ListNode | null = null;
+
+  while (node != null) {
+    nextNode = node.next;
+    node.next = prevNode;
+    prevNode = node;
+    node = nextNode;
+  }
+
+  return prevNode!;
+};