StackUsingQueuePopEfficient.java

packagesection11_Queue;

importjava.util.LinkedList;
importjava.util.Queue;

publicclassStackUsingQueuePopEfficient {

Queue<Integer> primary;
Queue<Integer> secondary;

publicStackUsingQueuePopEfficient() {
primary = newLinkedList<Integer>();
secondary = newLinkedList<Integer>();
 }

// O(1) Time
publicintpop() {
returnprimary.poll();
 }

// O(N) Time
publicvoidpush(intitem) {
secondary.add(item);
while (!primary.isEmpty()) {
secondary.add(primary.poll());
 }

// pointing primary queue to secondary queue and vice-versa
Queue<Integer> temp = secondary;
secondary = primary;
primary = temp;
 }

// O(1) Time
publicinttop() {
returnprimary.peek();
 }

publicintsize() {
returnprimary.size();
 }
}