单向链表

class Node {
    constructor(value) {
        this.value = value;
        this.next = null;
    }
}

class LinkedList {
    constructor() {
        this.count = 0;
        this.head = null;
    }
    // 链表尾部追加元素
    append(value) {
        let newNode = new Node(value);
        if (this.head === null) {
            this.head = newNode;
        } else {
            let currentNode = this.getElementAt(this.count - 1);
            currentNode.next = newNode;
        }
        this.count++;
    }
    // 在指定位置插入元素，越界返回false，表示插入失败
    insert(index, value) {
        if (index < 0 || index > this.count) {
            return false;
        }
        let newNode = new Node(value);

        if (this.head === null) {
            this.head = newNode;
        } else if (index === 0) {
            newNode.next = this.head;
            this.head = newNode;
        } else {
            let lastNode = this.getElementAt(index - 1);
            newNode.next = lastNode.next;
            lastNode.next = newNode;
        }
        this.count++;
        return true;
    }
    // 移除指定元素。若找不到该元素，则返回false，表示移除失败
    remove(value) {
        let lastNode = null;
        let currentNode = this.head;
        while (currentNode) {
            if (currentNode.value === value) {
                if (lastNode === null) {
                    this.head = this.head.next;
                } else {
                    lastNode.next = currentNode.next;
                }
                this.count--;
                return true;
            }
            lastNode = currentNode;
            currentNode = currentNode.next;
        }
        return false;
    }
    // 移除指定位置上的元素。若找不到该位置，则返回false，表示移除失败
    removeAt(index) {
        if (index < 0 || index > this.count - 1) {
            return false;
        }
        if (index === 0) {
            this.head = this.head.next;
        } else {
            let lastNode = this.getElementAt(index - 1);
            lastNode.next = lastNode.next.next;
        }
        this.count--;
        return true;
    }
    // 返回指定位置的节点，越界返回undefined
    getElementAt(index) {
        if (index < 0 || index >= this.count) {
            return undefined;
        }
        let currentNode = this.head;
        for (let i = 0; i < index; i++) {
            currentNode = currentNode.next;
        }
        return currentNode;
    }
    // 返回元素的索引值，若没改元素则返回-1
    indexOf(value) {
        let currentNode = this.head;
        let index = 0;
        while (currentNode) {
            if (currentNode.value === value) {
                return index;
            }
            currentNode = currentNode.next;
            index++;
        }
        return -1;
    }
    // 返回链表元素个数
    size() {
        return this.count;
    }
    // 返回当前是否为空链表
    isEmpty() {
        return this.count === 0
    }
    // 清空链表
    clear() {
        this.count = 0;
        this.head = null;
    }
    // 输出链表每项元素
    toString() {
        let arr = [];
        let currentNode = this.head;
        while (currentNode) {
            arr.push(currentNode.value);
            currentNode = currentNode.next;
        }
        return arr.join(",")
    }
}


let linkedList = new LinkedList();
linkedList.append(1)
linkedList.append(3)
linkedList.append(5)
linkedList.append(7)
linkedList.insert(1, 2)
linkedList.insert(2, 0)
linkedList.insert(1, 10)
console.log(linkedList.toString())
// console.log(linkedList.indexOf(0))
// console.log(linkedList.removeAt(1))
console.log(linkedList.remove(7))
console.log(linkedList.toString())
// console.log(linkedList.insert(linkedList.size(), 1000))
// console.log(linkedList.toString())