JavaScript implements double-ended queue

This article example shares the specific code of javascript to implement double-ended queues for your reference. The specific content is as follows

1. Double-ended queue

A deque is a special queue that allows us to add and remove elements from both the front and back ends at the same time.

2. Application of double-ended queues

If a person who has just bought a ticket needs to ask some simple information, he can go back to the head of the line. If the person at the end of the line is in a hurry, he can leave the line.

3. Double-ended queue method

addFront(element): This method adds a new element to the front of the double-ended queue
addBack(element): This method adds a new element to the back end of the double-ended queue (the implementation method is the same as the enqueue method in the Queue class).
removeFront(): This method removes the first element from the front of the double-ended queue
removeBack(): This method removes the first element from the back end of the double-ended queue
peekFront(): This method returns the first element of the double-ended queue.
peekBack()): This method returns the first element at the back end of the double-ended queue.

4. Implementation

class Deque{
           constructor(){
               this.items = {};
               this.count = 0;
               this.lowestCount = 0; 
           }

        // Add a new element to the front of the double-ended queue addFront(element){
            if(this.isEmpty()){
                this.addBack(element);
            }
            else if(this.lowestCount > 0){
                this.lowestCount --;
                this.items[this.lowestCount] = element;
            }
            else{
                for(let i=this.count;i>0;i--){
                    this.items[i] = this.items[i-1]; 
                }
                this.lowestCount = 0;
                this.items[this.lowestCount] = element;
                this.count++;
            }
        };
        addBack(element){
            this.count++;
            this.items[this.count-1] = element;
        };
        removeFront(){
            if(this.isEmpty()){
                return undefined;
            }
            const result = this.items[this.lowestCount];
            delete this.items[this.lowestCount];
            this.lowestCount++;
            return result;
        };
        removeBack(){
            if(this.isEmpty()){
                return undefined;
            }
            const result = this.items[this.count-1];
            delete this.items[this.count-1];
            this.count--;
            return result;
        };
        peekFront(){
            if(this.isEmpty()){
                return null;
            }
          return this.items[this.lowestCount];
        };
        peekBack(){
            if(this.isEmpty()){
                return null;
            }
            return this.items[this.count-1];
        };
        isEmpty(){
            return this.count - this.lowestCount == 0;
        }
        size(){
            return this.count - this.lowestCount;
        }
        toString(){
            if(this.isEmpty()){
                return '';
            }
            let objString = `${this.items[this.lowestCount]}`;
            for(var i=this.lowestCount+1;i<this.count;i++){
                objString = `${objString},${this.items[i]}`;
            }
            return objString;
        }
        clear(){
            this.items={};
            this.count = 0;
            this.lowestCount = 0;
        }
   

       }

       const deque = new Deque();
       deque.addFront('John');
       deque.addFront('Jack');
       deque.addFront('Amy');
       deque.addBack('Lisa');
    // deque.removeFront();
    // deque.removeBack();
    console.log(deque.size());
    console.log(deque.toString());
    console.log(deque);
    console.log(deque.isEmpty());
       console.log(deque.clear());
       console.log(deque);

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