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Merged
anirudhmurali merged 1 commit into from
Apr 29, 2020
Merged

IntQueue #1289

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111 changes: 111 additions & 0 deletions src/main/java/com/dataStructures/IntQueue.java
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package com.dataStructures;

/**
* This file contains an implementation of an integer only queue which is extremely quick and
* lightweight. In terms of performance it can outperform java.util.ArrayDeque (Java's fastest queue
* implementation) by a factor of 40+! See the benchmark test below for proof. However, the downside
* is you need to know an upper bound on the number of elements that will be inside the queue at any
* given time for this queue to work.
*
*
*/


public class IntQueue {

private int[] ar;
private int front, end, sz;

// maxSize is the maximum number of items
// that can be in the queue at any given time
public IntQueue(int maxSize) {
front = end = 0;
sz = maxSize + 1;
ar = new int[sz];
}

// Return true/false on whether the queue is empty
public boolean isEmpty() {
return front == end;
}

// Return the number of elements inside the queue
public int size() {
if (front > end) return (end + sz - front);
return end - front;
}

public int peek() {
return ar[front];
}

// Add an element to the queue
public void enqueue(int value) {
ar[end] = value;
if (++end == sz) end = 0;
if (end == front) throw new RuntimeException("Queue too small!");
}

// Make sure you check is the queue is not empty before calling dequeue!
public int dequeue() {
int ret_val = ar[front];
if (++front == sz) front = 0;
return ret_val;
}

// Example usage to check the how fast this implementation is
public static void main(String[] args) {

IntQueue q = new IntQueue(5);

q.enqueue(1);
q.enqueue(2);
q.enqueue(3);
q.enqueue(4);
q.enqueue(5);

System.out.println(q.dequeue()); // 1
System.out.println(q.dequeue()); // 2
System.out.println(q.dequeue()); // 3
System.out.println(q.dequeue()); // 4

System.out.println(q.isEmpty()); // false

q.enqueue(1);
q.enqueue(2);
q.enqueue(3);

System.out.println(q.dequeue()); // 5
System.out.println(q.dequeue()); // 1
System.out.println(q.dequeue()); // 2
System.out.println(q.dequeue()); // 3

System.out.println(q.isEmpty()); // true

benchMarkTest();
}

// BenchMark IntQueue vs ArrayDeque.
private static void benchMarkTest() {

int n = 10000000;
IntQueue intQ = new IntQueue(n);

// IntQueue times at around 0.0324 seconds
long start = System.nanoTime();
for (int i = 0; i < n; i++) intQ.enqueue(i);
for (int i = 0; i < n; i++) intQ.dequeue();
long end = System.nanoTime();
System.out.println("IntQueue Time: " + (end - start) / 1e9);

// ArrayDeque times at around 1.438 seconds
java.util.ArrayDeque<Integer> arrayDeque = new java.util.ArrayDeque<>();
// java.util.ArrayDeque <Integer> arrayDeque = new java.util.ArrayDeque<>(n); // strangely the
// ArrayQueue is slower when you give it an initial capacity.
start = System.nanoTime();
for (int i = 0; i < n; i++) arrayDeque.offer(i);
for (int i = 0; i < n; i++) arrayDeque.poll();
end = System.nanoTime();
System.out.println("ArrayDeque Time: " + (end - start) / 1e9);
}
}
128 changes: 128 additions & 0 deletions src/test/java/com/dataStructures/IntQueueTest.java
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package com.dataStructures;

import static org.junit.Assert.*;

import java.util.*;
import org.junit.Before;
import org.junit.Test;

public class IntQueueTest {

@Before
public void setup() {}

@Test
public void testEmptyQueue() {
IntQueue queue = new IntQueue(0);
assertTrue(queue.isEmpty());
assertEquals(queue.size(), 0);
}



@Test
public void testEnqueueOneElement() {
IntQueue queue = new IntQueue(1);
queue.enqueue(77);
assertEquals(queue.size(), 1);
}

@Test
public void testAll() {
int n = 5;
IntQueue queue = new IntQueue(10);
assertTrue(queue.isEmpty());
for (int i = 1; i <= n; i++) {
queue.enqueue(i);
assertFalse(queue.isEmpty());
}
for (int i = 1; i <= n; i++) {
assertEquals(i, queue.peek());
assertEquals(i, queue.dequeue());
assertEquals(queue.size(), n - i);
}
assertTrue(queue.isEmpty());
n = 8;
for (int i = 1; i <= n; i++) {
queue.enqueue(i);
assertFalse(queue.isEmpty());
}
for (int i = 1; i <= n; i++) {
assertEquals(i, queue.peek());
assertEquals(i, queue.dequeue());
assertEquals(queue.size(), n - i);
}
assertTrue(queue.isEmpty());
n = 9;
for (int i = 1; i <= n; i++) {
queue.enqueue(i);
assertFalse(queue.isEmpty());
}
for (int i = 1; i <= n; i++) {
assertEquals(i, queue.peek());
assertEquals(i, queue.dequeue());
assertEquals(queue.size(), n - i);
}
assertTrue(queue.isEmpty());
n = 10;
for (int i = 1; i <= n; i++) {
queue.enqueue(i);
assertFalse(queue.isEmpty());
}
for (int i = 1; i <= n; i++) {
assertEquals(i, queue.peek());
assertEquals(i, queue.dequeue());
assertEquals(queue.size(), n - i);
}
assertTrue(queue.isEmpty());
}

@Test
public void testPeekOneElement() {
IntQueue queue = new IntQueue(1);
queue.enqueue(77);
assertTrue(queue.peek() == 77);
assertEquals(queue.size(), 1);
}

@Test
public void testDequeueOneElement() {
IntQueue queue = new IntQueue(1);
queue.enqueue(77);
assertTrue(queue.dequeue() == 77);
assertEquals(queue.size(), 0);
}

@Test
public void testRandom() {

for (int qSize = 1; qSize <= 50; qSize++) {

IntQueue intQ = new IntQueue(qSize);
ArrayDeque<Integer> javaQ = new ArrayDeque<>(qSize);

assertEquals(javaQ.isEmpty(), intQ.isEmpty());
assertEquals(javaQ.size(), intQ.size());

for (int operations = 0; operations < 5000; operations++) {

double r = Math.random();

if (r < 0.60) {
int elem = (int) (1000 * Math.random());
if (javaQ.size() < qSize) {
javaQ.offer(elem);
intQ.enqueue(elem);
}
} else {
if (!javaQ.isEmpty()) {
assertEquals((int) javaQ.poll(), (int) intQ.dequeue());
}
}

assertEquals(javaQ.isEmpty(), intQ.isEmpty());
assertEquals(javaQ.size(), intQ.size());
}
}
}
}