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Add Java queue, stack, deque examples wits usage #29

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Add Java queue, stack, deque examples wits usage #29

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123 changes: 123 additions & 0 deletions Java/DequeExample.java
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Original file line number Diff line number Diff line change
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package Java;

import java.util.Arrays;

public class DequeExample {

static class Deque {

private Element first;

private Element last;

private int count;

public void push(final String value) {
final Element element = new Element(last, null, value);
last = element;
count++;
if (count == 1) {
first = last;
} else {
last.prev.next = element;
}

}

public String pop() {
if (count == 0) {
throw new NullPointerException("Deque is empty");
}
final Element result = last;
last = last.prev;
count--;
if (count == 0 || count == 1) {
first = last;
} else {
last.next = null;
}
return result.value;
}

public void unshift(final String value) {
final Element element = new Element(null, first, value);
first = element;
count++;
if (count == 1) {
last = first;
} else {
first.next.prev = element;
}
}

public String shift() {
if (count == 0) {
throw new NullPointerException("Deque is empty");
}
final Element result = first;
first = first.next;
count--;
if (count == 0 || count == 1) {
last = first;
} else {
first.prev = null;
}
return result.value;
}

public String[] asArray() {
final String[] result = new String[count];
Element current = first;
for (int i = 0; i < count; i++) {
result[i] = current.value;
current = current.next;
}
return result;
}


private static class Element {

private Element prev;

private Element next;

private final String value;

private Element(final Element prev,
final Element next,
final String value) {
this.prev = prev;
this.next = next;
this.value = value;
}
}
}

// Usage
public static void main(final String[] args) {
final Deque list = new Deque();
list.push("first");
list.push("second");
list.push("third");

String[] array = list.asArray();
System.out.println(Arrays.toString(array));

System.out.println(list.pop());
System.out.println(list.pop());
System.out.println(list.pop());

list.unshift("first");
list.unshift("second");
list.unshift("third");

array = list.asArray();
System.out.println(Arrays.toString(array));

System.out.println(list.shift());
System.out.println(list.shift());
System.out.println(list.shift());
//System.out.println(list.unshift());
}
}
82 changes: 82 additions & 0 deletions Java/QueueExample.java
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package Java;

import java.util.Arrays;

/**
* @author Michael Balakhon
* @link t.me/mibal_ua.
*/
public class QueueExample {

static class Queue {

private Element first;

private Element last;

private int count;

public void put(final String value) {
final Element element = new Element(first, value);
if (count == 0) {
first = element;
} else {
last.next = element;
}
last = element;
count++;
}

public String pick() {
if (count == 0) {
throw new NullPointerException("Queue is empty");
}
final Element result = first;
first = first.next;
count--;
if (count == 0 || count == 1) {
last = first;
}
return result.value;
}

public String[] asArray() {
final String[] result = new String[count];
Element current = first;
for (int j = 0; j < count; j++) {
result[j] = current.value;
current = current.next;
}
return result;
}


private static class Element {

private Element next;

private final String value;

public Element(final Element next, final String value) {
this.next = next;
this.value = value;
}
}
}

// Usage
public static void main(final String[] args) {
final Queue queue = new Queue();
queue.put("first");
queue.put("second");
queue.put("third");

String[] array = queue.asArray();
System.out.println(Arrays.toString(array));

System.out.println(queue.pick());
System.out.println(queue.pick());
System.out.println(queue.pick());
//System.out.println(queue.pick());
}
}
67 changes: 67 additions & 0 deletions Java/StackExample.java
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package Java;

import java.util.Arrays;

public class StackExample {

static class Stack {

private Element last;

private int count;

public void push(final String value) {
last = new Element(last, value);
count++;
}

public String pop() {
if (count == 0) {
throw new NullPointerException("Stack is empty");
}
final Element result = last;
last = last.prev;
count--;
return result.value;
}

public String[] asArray() {
final String[] result = new String[count];
Element current = last;
for (int i = count - 1; i >= 0; i--) {
result[i] = current.value;
current = current.prev;
}
return result;
}


private static class Element {

private final Element prev;

private final String value;

public Element(final Element prev, final String value) {
this.prev = prev;
this.value = value;
}
}
}

// Usage
public static void main(final String[] args) {
final Stack stack = new Stack();
stack.push("first");
stack.push("second");
stack.push("third");

String[] array = stack.asArray();
System.out.println(Arrays.toString(array));

System.out.println(stack.pop());
System.out.println(stack.pop());
System.out.println(stack.pop());
//System.out.println(stack.pop());
}
}