Queues
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import java.util.Stack;
class Queue{
private Stack<String> stack=null;
private String firstElement=null;
public Queue(){
stack = new Stack<String>();
}
public boolean enqueue(String value){
if (value == null || value.isEmpty()){
System.out.println("The value to enqueue cannot be null or empty.");
return false;
}
if (firstElement == null){
firstElement= value;
}
stack.push(value);
return true;
}
public String dequeue(){
if (stack.isEmpty()){
System.out.println("CAnnot dequeue, the queue is empty.");
}
Stack<String> temporalReversedStack= new Stack<String>();
while (!stack.isEmpty()){
temporalReversedStack.push(stack.pop());
}
String removedValue = temporalReversedStack.pop();
firstElement = temporalReversedStack.peek();
while (!temporalReversedStack.isEmpty()){
stack.push(temporalReversedStack.pop());
}
return removedValue;
}
public String peek(){
if (stack.isEmpty()){
System.out.println("The queue is empty.");
return null;
}
return firstElement;
}
}
class Main {
public static void main(String[] args) {
Queue queue = new Queue();
queue.enqueue("1");
queue.enqueue("2");
queue.enqueue("3");
queue.dequeue();
System.out.println("Peek:"+ queue.peek());
}
}
Java
INFO