reverse-linked-list

Author: taewanseoul

reverse-linked-list/taewanseoul.ts

@@ -0,0 +1,45 @@
+/**
+ * 206. Reverse Linked List
+ * Given the head of a singly linked list, reverse the list, and return the reversed list.
+ *
+ * https://leetcode.com/problems/reverse-linked-list/description/
+ *
+ */
+
+/**
+ * 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)
+ *     }
+ * }
+ */
+
+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;
+  }
+}
+
+// O(n) time
+// O(1) space
+function reverseList(head: ListNode | null): ListNode | null {
+  let prev: ListNode | null = null;
+  let next: ListNode | null = null;
+
+  while (head) {
+    next = head.next;
+    head.next = prev;
+
+    prev = head;
+    head = next;
+  }
+
+  return prev;
+}