链表代码汇总（方便查阅）

单向节点

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

双向节点

export class DoublyNode extends Node {
  constructor(element, next, prev) {
    super(element, next);
    this.prev = prev;
  }
}

单向链表

export default class LinkedList {
  constructor(equalsFn = defaultEquals) {
    this.equalsFn = equalsFn;
    this.count = 0;
    this.head = undefined;
  }
  push(element) {
    const node = new Node(element);
    let current;
    if (this.head == null) {
      // catches null && undefined
      this.head = node;
    } else {
      current = this.head;
      while (current.next != null) {
        current = current.next;
      }
      current.next = node;
    }
    this.count++;
  }
  getElementAt(index) {
    if (index >= 0 && index <= this.count) {
      let node = this.head;
      for (let i = 0; i < index && node != null; i++) {
        node = node.next;
      }
      return node;
    }
    return undefined;
  }
  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 previous = this.getElementAt(index - 1);
        node.next = previous.next;
        previous.next = node;
      }
      this.count++;
      return true;
    }
    return false;
  }
  removeAt(index) {
    if (index >= 0 && index < this.count) {
      let current = this.head;
      if (index === 0) {
        this.head = current.next;
      } else {
        const previous = this.getElementAt(index - 1);
        current = previous.next;
        previous.next = current.next;
      }
      this.count--;
      return current.element;
    }
    return undefined;
  }
  remove(element) {
    const index = this.indexOf(element);
    return this.removeAt(index);
  }
  indexOf(element) {
    let current = this.head;
    for (let i = 0; i < this.size() && current != null; i++) {
      if (this.equalsFn(element, current.element)) {
        return i;
      }
      current = current.next;
    }
    return -1;
  }
  isEmpty() {
    return this.size() === 0;
  }
  size() {
    return this.count;
  }
  getHead() {
    return this.head;
  }
  clear() {
    this.head = undefined;
    this.count = 0;
  }
  toString() {
    if (this.head == null) {
      return '';
    }
    let objString = `${this.head.element}`;
    let current = this.head.next;
    for (let i = 1; i < this.size() && current != null; i++) {
      objString = `${objString},${current.element}`;
      current = current.next;
    }
    return objString;
  }
}

单向循环链表

export default class CircularLinkedList extends LinkedList {
  constructor(equalsFn = defaultEquals) {
    super(equalsFn);
  }
  push(element) {
    const node = new Node(element);
    let current;
    if (this.head == null) {
      this.head = node;
    } else {
      current = this.getElementAt(this.size() - 1);
      current.next = node;
    }
    // set node.next to head - to have circular list
    node.next = this.head;
    this.count++;
  }
  insert(element, index) {
    if (index >= 0 && index <= this.count) {
      const node = new Node(element);
      let current = this.head;
      if (index === 0) {
        if (this.head == null) {
          // if no node  in list
          this.head = node;
          node.next = this.head;
        } else {
          node.next = current;
          current = this.getElementAt(this.size());
          // update last element
          this.head = node;
          current.next = this.head;
        }
      } else {
        const previous = this.getElementAt(index - 1);
        node.next = previous.next;
        previous.next = node;
      }
      this.count++;
      return true;
    }
    return false;
  }
  removeAt(index) {
    if (index >= 0 && index < this.count) {
      let current = this.head;
      if (index === 0) {
        if (this.size() === 1) {
          this.head = undefined;
        } else {
          const removed = this.head;
          current = this.getElementAt(this.size() - 1);
          this.head = this.head.next;
          current.next = this.head;
          current = removed;
        }
      } else {
        // no need to update last element for circular list
        const previous = this.getElementAt(index - 1);
        current = previous.next;
        previous.next = current.next;
      }
      this.count--;
      return current.element;
    }
    return undefined;
  }
}

双向链表

export default class DoublyLinkedList extends LinkedList {
  constructor(equalsFn = defaultEquals) {
    super(equalsFn);
    this.tail = undefined;
  }
  push(element) {
    const node = new DoublyNode(element);
    if (this.head == null) {
      this.head = node;
      this.tail = node; // NEW
    } else {
      // attach to the tail node // NEW
      this.tail.next = node;
      node.prev = this.tail;
      this.tail = node;
    }
    this.count++;
  }
  insert(element, index) {
    if (index >= 0 && index <= this.count) {
      const node = new DoublyNode(element);
      let current = this.head;
      if (index === 0) {
        if (this.head == null) { // NEW
          this.head = node;
          this.tail = node; // NEW
        } else {
          node.next = this.head;
          this.head.prev = node; // NEW
          this.head = node;
        }
      } else if (index === this.count) { // last item NEW
        current = this.tail;
        current.next = node;
        node.prev = current;
        this.tail = node;
      } else {
        const previous = this.getElementAt(index - 1);
        current = previous.next;
        node.next = current;
        previous.next = node;
        current.prev = node; // NEW
        node.prev = previous; // NEW
      }
      this.count++;
      return true;
    }
    return false;
  }
  removeAt(index) {
    if (index >= 0 && index < this.count) {
      let current = this.head;
      if (index === 0) {
        this.head = this.head.next;
        // if there is only one item, then we update tail as well //NEW
        if (this.count === 1) {
          // {2}
          this.tail = undefined;
        } else {
          this.head.prev = undefined;
        }
      } else if (index === this.count - 1) {
        // last item //NEW
        current = this.tail;
        this.tail = current.prev;
        this.tail.next = undefined;
      } else {
        current = this.getElementAt(index);
        const previous = current.prev;
        // link previous with current's next - skip it to remove
        previous.next = current.next;
        current.next.prev = previous; // NEW
      }
      this.count--;
      return current.element;
    }
    return undefined;
  }
  indexOf(element) {
    let current = this.head;
    let index = 0;
    while (current != null) {
      if (this.equalsFn(element, current.element)) {
        return index;
      }
      index++;
      current = current.next;
    }
    return -1;
  }
  getHead() {
    return this.head;
  }
  getTail() {
    return this.tail;
  }
  clear() {
    super.clear();
    this.tail = undefined;
  }
  toString() {
    if (this.head == null) {
      return '';
    }
    let objString = `${this.head.element}`;
    let current = this.head.next;
    while (current != null) {
      objString = `${objString},${current.element}`;
      current = current.next;
    }
    return objString;
  }
  inverseToString() {
    if (this.tail == null) {
      return '';
    }
    let objString = `${this.tail.element}`;
    let previous = this.tail.prev;
    while (previous != null) {
      objString = `${objString},${previous.element}`;
      previous = previous.prev;
    }
    return objString;
  }
}

有序链表

export const Compare = {
  LESS_THAN: -1,
  BIGGER_THAN: 1,
  EQUALS: 0
};

export function defaultCompare(a, b) {
  if (a === b) {
    return Compare.EQUALS;
  }
  return a < b ? Compare.LESS_THAN : Compare.BIGGER_THAN;
}

export default class SortedLinkedList extends LinkedList {
  constructor(equalsFn, compareFn = defaultCompare) {
    super(equalsFn);
    this.compareFn = compareFn;
  }
  push(element) {
    if (this.isEmpty()) {
      super.push(element);
    } else {
      const index = this.getIndexNextSortedElement(element);
      super.insert(element, index);
    }
  }
  insert(element, index = 0) {
    if (this.isEmpty()) {
      return super.insert(element, index === 0 ? index : 0);
    }
    const pos = this.getIndexNextSortedElement(element);
    return super.insert(element, pos);
  }
  getIndexNextSortedElement(element) {
    let current = this.head;
    let i = 0;
    for (; i < this.size() && current; i++) {
      const comp = this.compareFn(element, current.element);
      if (comp === Compare.LESS_THAN) {
        return i;
      }
      current = current.next;
    }
    return i;
  }
}