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// Implement Queue interface using Stack interface as a storage

function queue() {
  this.stack = [];
}

queue.prototype.enq = function(item) {
  this.stack.push(item);
}

queue.prototype.deq = function() {
  if (this.stack.length == 0) {
    return null;
  }
  if (this.stack.length == 1) {
    return this.stack.pop();
  } else {
    let pulled = this.stack.pop();
    let res = this.deq();
    this.stack.push(pulled);
    return res;
  }
  
}

console.log('=====');
let q = new queue();
q.enq(1);
q.enq(2);
q.enq(3);
q.enq(4);

console.log(q.deq()); // 1
console.log(q.deq()); // 2
console.log(q.deq()); // 3
console.log(q.deq()); // 4
console.log(q.deq()); // null
console.log(q.deq()); // null
console.log(q.stack);