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Taleof2Stacks.java
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Taleof2Stacks.java
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import java.util.Scanner;
import java.util.Stack;
public class Taleof2Stacks {
static class MyQueue<T> {
Stack<T> newOnTop = new Stack<>();
Stack<T> oldOnTop = new Stack<>();
void enqueue(T item){
newOnTop.push(item);
}
T dequeue(){
if(oldOnTop.isEmpty())
fillOld();
return oldOnTop.pop();
}
T peek(){
if(oldOnTop.isEmpty())
fillOld();
return oldOnTop.peek();
}
void fillOld(){
if(!newOnTop.isEmpty()){
oldOnTop.push(newOnTop.pop());
}
}
}
public static void main(String[] args) {
MyQueue<Integer> queue = new Taleof2Stacks.MyQueue<>();
Scanner scan = new Scanner(System.in);
int n = scan.nextInt();
for (int i = 0; i < n; i++) {
int operation = scan.nextInt();
if (operation == 1) { // enqueue
queue.enqueue(scan.nextInt());
} else if (operation == 2) { // dequeue
queue.dequeue();
} else if (operation == 3) { // print/peek
System.out.println(queue.peek());
}
}
scan.close();
}
}