Implement the following operations of a queue using stacks.
push(x) -- Push element x to the back of queue.
pop() -- Removes the element from in front of queue.
peek() -- Get the front element.
empty() -- Return whether the queue is empty.
public class MyQueue {
Stack<Integer> stack1;
Stack<Integer> stack2;
/** Initialize your data structure here. */
public MyQueue() {
stack1 = new Stack<Integer>();
stack2 = new Stack<Integer>();
}
/** Push element x to the back of queue. */
public void push(int x) {
stack2.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
if(stack1.isEmpty() == true) {
stack2ToStack1();
}
if (stack1.isEmpty() != true) {
return stack1.pop();
} else {
return -1;
}
}
/** Get the front element. */
public int peek() {
if(stack1.isEmpty() == true) {
stack2ToStack1();
}
if (stack1.isEmpty() != true) {
return stack1.peek();
} else {
return -1;
}
}
/** Returns whether the queue is empty. */
public boolean empty() {
if(stack1.isEmpty() == true) {
stack2ToStack1();
}
return stack1.isEmpty();
}
private void stack2ToStack1() {
while (!stack2.empty()) {
stack1.push(stack2.pop());
}
}
}
