92.反转链表-ii

/*
 * @lc app=leetcode.cn id=92 lang=typescript
 *
 * [92] 反转链表 II
 */

// @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)
 *     }
 * }
 */

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 reverseBetween(
	head: ListNode | null,
	left: number,
	right: number
): ListNode | null {
	const newNode = new ListNode(0, head);

	let pre = newNode;
	// 找到right的前一位pre
	for (let i = 0; i < left - 1; i++) {
		pre = pre.next as ListNode; // 必存在
	}
	let cur = pre.next as ListNode;

	// 截止条件left>=right
	while (left < right) {
		// 将cur+1提到头部
		const next = cur.next as ListNode;
		cur.next = next.next;
		next.next = pre.next;
		pre.next = next;
		left++;
	}

	return newNode.next;
}

let tag1 = new ListNode(1);
let tag2 = new ListNode(2);
let tag3 = new ListNode(3);
let tag4 = new ListNode(4);
let tag5 = new ListNode(4);

tag1.next = tag2;
tag2.next = tag3;
tag3.next = tag4;
tag4.next = tag5;

console.log(reverseBetween(tag1, 2, 4));
// @lc code=end