206.reverse-linked-list.ts

/*
 * @lc app=leetcode id=206 lang=typescript
 *
 * [206] Reverse Linked List
 */

// @lc code=start
/**
 * 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 reverseList(head: ListNode | null): ListNode | null {
  let prev: ListNode = null;
  let cur: ListNode = head;

  while (cur != null) {
    let next: ListNode = cur.next;
    cur.next = prev;
    prev = cur;
    cur = next;
  }
  return prev;
}
// @lc code=end