Files
Java/src/main/java/com/thealgorithms/others/QueueUsingTwoStacks.java
Alex Klymenko 6b7a1fdbe8 refactor: QueueUsingTwoStacks (#5427)
refactor: QueueUsingTwoStacks

Co-authored-by: alxkm <alx@alx.com>
2024-08-28 22:25:46 +02:00

106 lines
2.6 KiB
Java

package com.thealgorithms.others;
import java.util.Stack;
/**
* This implements Queue using two Stacks.
*
* <p>
* Big O Runtime: insert(): O(1) remove(): O(1) amortized isEmpty(): O(1)
*
* <p>
* A queue data structure functions the same as a real world queue. The elements
* that are added first are the first to be removed. New elements are added to
* the back/rear of the queue.
*
* @author sahilb2 (https://www.github.com/sahilb2)
*/
public class QueueUsingTwoStacks {
private final Stack<Object> inStack;
private final Stack<Object> outStack;
/**
* Constructor
*/
public QueueUsingTwoStacks() {
this.inStack = new Stack<>();
this.outStack = new Stack<>();
}
/**
* Inserts an element at the rear of the queue
*
* @param x element to be added
*/
public void insert(Object x) {
// Insert element into inStack
this.inStack.push(x);
}
/**
* Remove an element from the front of the queue
*
* @return the new front of the queue
*/
public Object remove() {
if (this.outStack.isEmpty()) {
// Move all elements from inStack to outStack (preserving the order)
while (!this.inStack.isEmpty()) {
this.outStack.push(this.inStack.pop());
}
}
return this.outStack.pop();
}
/**
* Peek at the element from the front of the queue
*
* @return the front element of the queue
*/
public Object peekFront() {
if (this.outStack.isEmpty()) {
// Move all elements from inStack to outStack (preserving the order)
while (!this.inStack.isEmpty()) {
this.outStack.push(this.inStack.pop());
}
}
return this.outStack.peek();
}
/**
* Peek at the element from the back of the queue
*
* @return the back element of the queue
*/
public Object peekBack() {
return this.inStack.peek();
}
/**
* Returns true if the queue is empty
*
* @return true if the queue is empty
*/
public boolean isEmpty() {
return (this.inStack.isEmpty() && this.outStack.isEmpty());
}
/**
* Returns true if the inStack is empty.
*
* @return true if the inStack is empty.
*/
public boolean isInStackEmpty() {
return (inStack.isEmpty());
}
/**
* Returns true if the outStack is empty.
*
* @return true if the outStack is empty.
*/
public boolean isOutStackEmpty() {
return (outStack.isEmpty());
}
}