SOURCE

class Node {
    constructor(element) {
        this.element = element;
        this.next = undefined;
    }
}

function defaultEquals(a, b) {
    return a === b;
}

// 模拟链表类
class LinkedList {
    constructor(equalsFn = defaultEquals) {
        this.count = 0;
        this.head = undefined;
        this.equalsFn = equalsFn;
    }

    size() {
        return this.count
    }

    isEmpty() {
        return this.count === 0
    }

    getHead() {
        return this.head;
    }

    toString() {
        if (this.count === 0) {
            return ''
        }
        // 类似于数组的join方法
        let str = `${this.head.element}`;
        let current = this.head.next;
        for (let i = 1; i < this.count && current !== undefined; i++) {
            str = `${str}, ${current.element}`;
            current = current.next;
        }
        return str;
    }

    // 添加元素
    push(element) {
        const node = new Node(element);
        let current;
        if (this.head === undefined) {
            this.head = node;
        } else {
            current = this.head;
            while (current.next !== undefined) {
                current = current.next;
            }
            // 将其 next 赋为新元素，建立链接
            current.next = node;
        }
        this.count++;
    }

    // 通过序号获取元素
    getElementAt(index) {
        // 是否是多余的判断
        if (index >= 0 && index < this.count) {
            let node = this.head;
            for (let i = 0; i < index && node !== undefined; i++) {
                node = node.next;
            }
            return node;
        }
        return undefined;
    }

    // 按序号移除元素
    removeAt(index) {
        // 检查越界值
        if (index >= 0 && index < this.count) {
            let current = this.head;
            // 移除第一项
            if (index === 0) {
                this.head = current.next;
            } else {
                const prevNode = this.getElementAt(index - 1);
                current = prevNode.next;
                // 将prevNode与current的下一项链接起来:跳过current，从而移除它
                prevNode.next = current.next;
            }
            this.count--;
            return current.element;
        }
        return undefined;
    }

    // 返回一个元素的位置
    indexOf(element) {
        let current = this.head;
        for (let i = 0; i < this.count && current !== undefined; i++) {
            if (this.equalsFn(current.element, element)) {
                return i;
            }
            current = current.next;
        }
        return -1;
    }

    // 移除元素
    remove(element) {
        const index = this.indexOf(element);
        return this.removeAt(index);
    }

    // 在任意位置插入元素
    insert(element, index) {
        if (index >= 0 && index <= this.count) {
            const node = new Node(element);
            if (index === 0) {
                const current = this.head;
                node.next = current;
                this.head = node;
            } else {
                const prevNode = this.getElementAt(index - 1);
                const current = prevNode.next;
                prevNode.next = node;
                node.next = current;
            }
            this.count++;
            return true;
        }
        return false;
    }
}

const link = new LinkedList()
console.log('长度', link.size())
console.log('是否为空', link.isEmpty())
link.push('ross')
link.push('jack')
link.push('roma')
console.log('长度', link.size())
console.log('是否为空', link.isEmpty())
console.log('删除第一个元素', link.removeAt(0))
console.log('长度', link.size())
console.log('在节点2插入一个元素', link.insert('new', 2))
console.log(link.toString())
console.log('获取roma位置', link.indexOf('roma'))
console.log('删除', link.remove('roma'))
console.log('长度', link.size())
console.log(link.toString())