class Queue {
  constructor(len) {
    this.array = [];
    this.arrayLen = len;
    this.front = null;
    this.rear = null;
    this.start();
  }
  start() {
    for (let i = 1; i <= this.arrayLen; i++) {
      this.array[i] = null;
    }
  }
  arrayN() {
    let count = 0;
    for (let i = 1; i <= this.arrayLen; i++) {
      if (this.array[i] == null) {
        continue;
      } else {
        count = count + 1;
      }
    }
    return count;
  }

  insert(data) {
    if (
      (this.front == 1 && this.rear == this.arrayLen) ||
      this.front == this.rear + 1
    ) {
      return "OVERFLOW";
    }
    if (this.front == null) {
      this.front = 1;
      this.rear = 1;
    } else if (this.rear == this.arrayLen) {
      this.rear = 1;
    } else {
      this.rear = this.rear + 1;
    }
    this.array[this.rear] = data;
  }

  remove() {
    if (this.front == null) {
      return "UNDERFLOW";
    } else {
      this.array[this.front] = null;
    }

    if (this.front == this.rear) {
      this.front = null;
      this.rear = null;
    } else if (this.front == this.arrayLen) {
      this.front = 1;
    } else {
      this.front = this.front + 1;
    }
  }
  isEmpty() {
    for (let i = 1; i <= this.arrayLen; i++) {
      if (this.array[i] != null) {
        return false;
      }
    }
    return true;
  }

}