雙向連結串列

雙向連結串列的 remove() 方法比單向連結串列的效率更高，因為不需要再查詢前驅節點了

//建立建構函式建立節點
function Node(element){
    this.element = element;
    this.next = null;
    this.previous = null;
    this.findLast = findLast;
    this.disPreverse = disPreverse;
}
//連結串列的建構函式
 function LList(){
    this.head = new Node('head');
    this.insert = insert;
    this.remove = remove;
    this.display = display;
    this.find = find;
 }
 function insert(newElement,item){
    var cur = this.find(item);
    var node = new Node(newElement);
    if(cur == null){
        alert('沒有找到插入位置');
    }else{
        node.next = cur.next;
        node.previous = cur;
        cur.next = node;
 

    }
 }
 function find(item){
    var cur = this.head;
    while(cur.element != item){
        cur = cur.next;
    }
    return cur;
 }
 function display() {
     var cur = this.head;
     var str = '';
     while (cur.next != null){
        str += cur.next.element+'->';
        cur = cur.next;
     }
     return str;
 }
 function remove(item){
    var cur = this.find(item);
    if(cur.next != null){
        cur.previous.next = cur.next;
        cur.next.previous = cur.previous;
        cur.next = null;
        cur.previous = null;
    }else{
        //注意，當節點的後繼為null時不要設定cur.next.previous = cur.previous
        //因為雙向連結串列中null時沒有前驅的，不能設定null的前驅
 

        cur.previous.next = null;
    }
    
 }
 //查詢最後一個節點
function findLast(){
    var cur = this.head;
    while(cur.next != null){
        cur = cur.next;
    }
    return cur;
}
//反序輸出節點
function disPreverse(){
    //注意，findLast()即使沒有引數也要帶括號
    //如果不帶括號，last則是一個function物件
    var last = this.findLast();
    //console.log(last);
    var str = '';
    while(last.previous != null){
        str += last.element+'->';
        last = last.previous;
    }
    return str;
}