QueueUsingStackEnqueueEfficient.java

packagesection11_Queue;

importjava.util.Stack;

publicclassQueueUsingStackEnqueueEfficient {

Stack<Integer> primary;
Stack<Integer> secondary;

publicQueueUsingStackEnqueueEfficient() {
primary = newStack<Integer>();
secondary = newStack<Integer>();
 }

// O(1) Time
publicvoidenqueue(intitem) {
primary.push(item);
 }

// O(N) Time
publicintdequeue() {
while (primary.size() != 1) {
secondary.push(primary.pop());
 }

intremovedItem = primary.pop();

while (!secondary.isEmpty()) {
primary.push(secondary.pop());
 }

returnremovedItem;
 }

// O(N) Time
publicintfront() {
while (primary.size() != 1) {
secondary.push(primary.pop());
 }

intfront = primary.peek();

while (!secondary.isEmpty()) {
primary.push(secondary.pop());
 }

returnfront;
 }

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