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queue.js
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queue.js
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/*
QUEUE
Abstract data type
FIFO - First in, first out
Collection of elements with enqueue and dequeue operations.
Note that there is a natural order. Elements are removed in the reverse order of their addition.
DO NOT use an array and the native push/shift method in your implementation. Use an object as the underlying data structure.
*** Operations:
myQueue.enqueue(value)
=> count of queue
add value to collection
myQueue.dequeue()
=> oldest element added collection
Remove item so that it is no longer in collection
myQueue.peek()
=> oldest element added collection
Similiar to dequeue, but do not remove element from collection
myQueue.count()
=> number of elements in queue
*** Exercises:
Modify your queue to take a max capacity and return a string if you try to add an element when there's no more room:
myQueue.enqueue(value)
=> "Max capacity already reached. Remove element before adding a new one."
Create a contains method to check if a value is in the queue:
myQueue.contains('findme')
=> true/false
What's the time complexity?
Create an until method to get the number of dequeues until you get to a certain value:
queue values - (first)2-5-7-3-6-9(last)
myQueue.until(7)
=> 3
What's the time complexity?
Implement a queue using two stacks (include enqueue, dequeue, peek, and count).
*/
function Queue(capacity) {
this._capacity = capacity || Infinity;
this._storage = {};
this._head = 0;
this._tail = 0;
}
// O(1)
Queue.prototype.enqueue = function(value) {
if (this.count() < this._capacity) {
this._storage[this._tail++] = value;
return this.count();
}
return 'Max capacity already reached. Remove element before adding a new one.';
};
// O(1)
Queue.prototype.dequeue = function() {
var element = this._storage[this._head];
delete this._storage[this._head];
if (this._head < this._tail) this._head++;
return element;
};
// O(1)
Queue.prototype.peek = function() {
return this._storage[this._head];
}
// O(1)
Queue.prototype.count = function() {
return this._tail - this._head;
};
// O(n)
Queue.prototype.contains = function(value) {
for (var i = this._head; i < this._tail; i++) {
if (this._storage[i] === value) return true;
}
return false;
};
// O(n)
Queue.prototype.until = function(value) {
for (var i = this._head; i < this._tail; i++) {
if (this._storage[i] === value) return i-this._head+1;
}
return null;
};
// var myQueue = new Queue(3);
// console.log(myQueue.enqueue('a'), 'should be 1');
// console.log(myQueue.enqueue('b'), 'should be 2');
// console.log(myQueue.enqueue('c'), 'should be 3');
// console.log(myQueue.enqueue('d'), 'should be Max capacity reached');
// console.log(myQueue.dequeue(), 'should be a');
// console.log(myQueue.count(), 'should be 2');
// console.log(myQueue.peek(), 'should be b');
// console.log(myQueue.count(), 'should be 2');
// console.log(myQueue.contains('b'), 'should be true');
// console.log(myQueue.contains('d'), 'should be false');
// console.log(myQueue._storage, myQueue._head);
// console.log(myQueue.until('b'), 'should be 1');
// console.log(myQueue.until('c'), 'should be 2');
// console.log(myQueue.until('d'), 'should be null');
// ____________________________________________
// EXERCISES
// Implement a queue using two stacks
function Stack(capacity) {
this._capacity = capacity || Infinity;
this._storage = {};
this._count = 0;
}
Stack.prototype.push = function(value) {
if (this._count < this._capacity) {
this._storage[this._count++] = value;
return this._count;
}
return 'Max capacity already reached. Remove element before adding a new one.';
};
Stack.prototype.pop = function() {
var value = this._storage[--this._count];
delete this._storage[this._count];
if (this._count < 0) {
this._count = 0;
}
return value;
};
Stack.prototype.peek = function() {
return this._storage[this._count-1];
}
Stack.prototype.count = function() {
return this._count;
};
function Queue_TwoStacks() {
this._stackIn = new Stack();
this._stackOut = new Stack();
}
Queue_TwoStacks.prototype.enqueue = function(val) {
this._stackIn.push(val);
};
Queue_TwoStacks.prototype._transferStacks = function() {
while (this._stackIn.count() > 0) {
this._stackOut.push(this._stackIn.pop());
}
};
Queue_TwoStacks.prototype.dequeue = function() {
if (this._stackOut.count() === 0) this._transferStacks();
return this._stackOut.pop();
};
Queue_TwoStacks.prototype.count = function() {
return this._stackIn.count() + this._stackOut.count();
};
Queue_TwoStacks.prototype.peek = function() {
if (this._stackOut.count() === 0) this._transferStacks();
return this._stackOut.peek();
};
// var myQueue_TwoStacks = new Queue(3);
// console.log(myQueue_TwoStacks.enqueue('a'), 'should be 1');
// console.log(myQueue_TwoStacks.enqueue('b'), 'should be 2');
// console.log(myQueue_TwoStacks.enqueue('c'), 'should be 3');
// console.log(myQueue_TwoStacks.enqueue('d'), 'should be Max capacity reached');
// console.log(myQueue_TwoStacks.dequeue(), 'should be a');
// console.log(myQueue_TwoStacks.count(), 'should be 2');
// console.log(myQueue_TwoStacks.peek(), 'should be b');
// console.log(myQueue_TwoStacks.count(), 'should be 2');