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QueueUsingStack.java

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package queue;

import java.util.Stack;

public class QueueUsingStack {

private Stack<Integer> stack1;

private Stack<Integer> stack2;

public QueueUsingStack() {

this.stack1 = new Stack<>();

this.stack2 = new Stack<>();

}

public void push(Integer item) {

stack1.push(item);

}

public Integer pop() {

if (stack2.isEmpty()) {

while (!stack1.isEmpty()) {

stack2.push(stack1.pop());

}

}

if (stack2.isEmpty()) {

throw new RuntimeException("Queue is empty");

}

return stack2.pop();

}

public boolean isEmpty() {

return stack1.isEmpty() && stack2.isEmpty();

}

}