JavaScript实现循环链表

单链表地址：点我

一、循环链表

　　节点的next指向下一个节点，节点的prev指向上一个节点

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function loopList() {     let length = 0,         head = null,         tail = null     this.append = (data) => {         let node = new Node(data),             current         if(head === null) {             head = node             tail = node         }else {             current = head             while(current.next) {                 current = current.next             }             current.next = node             tail = node         }         length ++         return true     }     this.insert = (position, data) => {         if(position > -1 && position <= length) {             let node = new Node(data),                 current = head,                 previous             if(position === 0) {                 if (!head) {                     head = node                     tail = node                 }else {                     node.next = current                     current.prev = node                     head = node                 }             }             else if(position === length) {                 current = tail                 current.next = node                 node.prev = current                 tail = node             }             else {                 while(index ++ < position) {                     previous = current                     current = current.next                 }                 previous.next = node                 node.prev = previous                 node.next = current                 current.prev = node             }             length ++             return true         }else {             return false         }     }     this.removePos = function (position) {         //检查是否越界         if (position > -1 && position < length) {             var current = head,                 previous,                 index = 0               if (position === 0) { //移除第一项                 head = current.next                 if (length === 1) {                     tail = null                 }else {                     head.prev = null                 }             }else if(position === length - 1) {                 current = tail                 tail = current.prev                 tail.next = null             }else {                 while (index++ < position) {                     previous = current                     current = current.next                 }                 //将previous与current的下一项链接起来，跳过current，从而移除它                 previous.next = current.next                 current.next.prev = previous             }             length --             return true         }else {             return false         }     }     this.removeData = (data) => {         if(head === null) {             return false         }         else {             let current = head,                 previous,                 index = 0             if (length === 1 ) {                 if (current.data !== data) {                     return false                 }else {                     head = null                     tail = null                     length --                     return true                 }             }                             while (index ++ < length && current.data !== data) {                 previous = current                 current = current.next             }             if(index === length) {                 current = tail                 tail = current.prev                 tail.next = null                 length --                 return true             }             if(index > length) {                 return false             }else {                 previous.next = current.next                 current.next.prev = previous                 length --                 return true             }         }     }     this.toString = () => {         let resultStr = "",             current,             index = length         if(head === null) {             return ""         }else {             current = head             while(index -- > 0) {                 resultStr += "," + current.data                 current = current.next             }             return resultStr.slice(1)         }     } }   function Node(data) {     this.data = data     this.next = null     this.prev = null }