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queueStacks.java
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queueStacks.java
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import java.util.*;
//FORM A QUEUE USING 2 STACKS (MAKING FIFO STRUCTURE USING LIFO STRUCTURE )
public class queueStacks {
static class Queue {
static Stack<Integer> s1 = new Stack<>();
static Stack<Integer> s2 = new Stack<>();
public static boolean isEmpty() {
return s1.isEmpty();
}
// ADD O(n)
public static void add(int data) {
while (!s1.isEmpty()) {
s2.push(s1.pop());
}
s1.push(data);
while (!s2.isEmpty()) {
s1.push(s2.pop());
}
}
// REMOVE O(1)
public static int remove() {
if (isEmpty()) {
System.out.println("queue empty");
return -1;
}
return s1.pop();
}
// PEEK O(1)
public static int peek() {
if (isEmpty()) {
System.out.println("queue empty");
return -1;
}
return s1.peek();
}
}
public static void main(String[] args) {
Queue q = new Queue();
q.add(1);
q.add(2);
q.add(3);
while (!q.isEmpty()) {
System.out.println(q.peek());
q.remove();
}
}
}