数据结构_双向链表

  //双向链表
  
  class Node {
    constructor (data) {
      this.data = data
      this.prev = null
      this.next = null
    }
  }

  class DoubleList {
    constructor () {
      this.head = null
      this.tail = null
      this.length = 0
    }
    //追加数据
    append (data) {
      //  创建新节点
      let newNode = new Node(data)
      // 链表为空
      if (!this.head) {
        this.head = newNode
        this.tail = newNode
      }else {
        newNode.prev = this.tail
        this.tail.next = newNode
        this.tail = newNode
      }
      this.length++
      return true
    }
    //插入数据
    insert (posi, data) {
      if (posi < 0 || posi > this.length) return false
      //创建新节点
      let newNode = new Node(data)
      if (posi == 0) {
        if (!this.head) {
          this.head = newNode
          this.tail = newNode
        }else {
          newNode.next = this.head
          this.head.prev = newNode
          this.prev = newNode
        }
      }else if (this.length == posi) {
        newNode.prev = this.tail
        this.tail.next = newNode
        this.tail = newNode
      }else {

        // 保存头节点
        // while (index++ < posi - 1) {
        //   current = current.next
        // }
        // newNode.prev = current
        // newNode.next = current.next
        // current.next.prev = newNode
        // current.next = newNode
        let current = ''
        let index = 0
        if (posi < this.length / 2) {
          current = this.head
          index = 0
          while (index++ < posi - 1) {
            current = current.next
          }
        }else {
          index = this.length - 1
          current = this.tail
          while (index-- > posi - 1) {
            current = current.prev
          }
        }
        newNode.next = current
        newNode.prev = current.prev
        current.prev.next = newNode
        current.prev = newNode

      }
      this.length++
      return true
    }
    //查找第一次出现的数据
    indexOf (data) {
      let current = this.head
      let index = 0
      while (current) {
        if (current.data === data) {
          return index
        }
        index++
        current = current.next
      }
      return -1
    }
    //查找到最后一次出现的数据
    lastIndexOf (data) {
      let current = this.tail
      let index = this.length - 1
      while (current) {
        if (current.data === data) {
          return index
        }
        index--
        current = current.prev
      }
      return -1
    }
    removeAt (posi) {
      if (posi < 0 || posi > this.length -1) return false
      if (posi == 0) {
        if (this.length == 1) {
          this.head = null
          this.tail = null
        }else {
          // this.head.next.prev = null
          // this.head = this.head.next
          this.head = this.head.next
          this.head.prev = null
        }
      }else if (posi == this.length - 1) {
        this.tail = this.tail.prev
        this.tail.next = null
      }else {
        let current = ''
        let index = 0
        if (posi < this.length / 2) {
          current = this.head
          index = 0
          while (index++ < posi - 1) {
            current = current.next
          }
        }else {
          index = this.length - 1
          current = this.tail
          while (index-- > posi - 1) {
            current = current.prev
          }
        }
        current.next = current.next.next
        current.next.prev = current
      }
      this.length--
      return true
    }
    remove (data) {
      //删除所有data的数据
      while (this.indexOf(data) != -1) {
        //删除第一个出现的data数据
        this.removeAt(this.index(data))
      }
      return true
    }
    isEmpty () {
      return this.head == null
    }
    size () {
      return this.length
    }
  }

  let dList = new DoubleList()
  dList.insert(0, 'a')
  dList.append('b')
  dList.append('c')
  dList.append('d')
  dList.append('e')
  dList.append('f')
  dList.append('g')
  dList.insert(4, 'h')
  dList.append('h')
  dList.removeAt(4)