面试题 02.01. 移除重复节点

/**
 * 编写代码，移除未排序链表中的重复节点。保留最开始出现的节点。
 * 示例1：
        输入：[1, 2, 3, 3, 2, 1]
        输出：[1, 2, 3]
 */

/**
 * 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 removeDuplicateNodes(head: ListNode | null): ListNode | null {
	let hashMap: Map<number, string> = new Map();

	let current = head; // 遍历用
	let p = head as ListNode; // 头
	while (current) {
		if (hashMap.has(current.val)) {
			// 已存在
			p.next = current.next;
		} else {
			// 不存在时
			p = current;
			hashMap.set(current.val, "c");
		}
		current = current.next;
	}
	return head;
}

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;
	}
}

let listTag1 = new ListNode(1);
let listTag2 = new ListNode(2);
let listTag3 = new ListNode(3);
let listTag4 = new ListNode(3);
let listTag5 = new ListNode(2);
let listTag6 = new ListNode(1);

listTag1.next = listTag2;
listTag2.next = listTag3;
listTag3.next = listTag4;
listTag4.next = listTag5;
listTag5.next = listTag6;

console.log(removeDuplicateNodes(listTag1));