Add reverse-linked-list solution in TypeScript

Author: Jeehay28

reverse-linked-list/Jeehay28.ts

@@ -0,0 +1,34 @@
+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;
+  }
+}
+
+// TC: O(n)
+// SC: O(1)
+function reverseList(head: ListNode | null): ListNode | null {
+  if (!head) return head;
+
+  //         1 -> 2 -> 3 -> 4 -> 5 -> null
+
+  // null <- 1
+  // prev   curr
+
+  // null <- 1 <- 2
+  //       prev  cur
+
+  let prev: ListNode | null = null;
+  let curr: ListNode | null = head;
+
+  while (curr) {
+    const tempNext: ListNode | null = curr.next; // 2 -> 3 -> 4 -> 5 -> null
+    curr.next = prev; // curr: 1 -> null
+    prev = curr; // curr: 1 -> null, 2 -> 1 -> null
+    curr = tempNext;
+  }
+
+  return prev;
+}