package it.unimi.dsi.fastutil;

/*
 * Copyright (C) 2002-2019 Sebastiano Vigna
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


import java.util.NoSuchElementException;

A stack.
A stack must provide the classical push(Object) and pop() operations, but may be also peekable to some extent: it may provide just the top() function, or even a more powerful peek(int) method that provides access to all elements on the stack (indexed from the top, which has index 0). /** A stack.
 *
 * <p>A stack must provide the classical {@link #push(Object)} and
 * {@link #pop()} operations, but may be also <em>peekable</em>
 * to some extent: it may provide just the {@link #top()} function,
 * or even a more powerful {@link #peek(int)} method that provides
 * access to all elements on the stack (indexed from the top, which
 * has index 0).
 */

public interface Stack<K> {

	
Pushes the given object on the stack.
Params:
o – the object that will become the new top of the stack./** Pushes the given object on the stack.
	 *
	 * @param o the object that will become the new top of the stack.
	 */

	void push(K o);

	
Pops the top off the stack.
Throws:
NoSuchElementException – if the stack is empty.
Returns:
the top of the stack./** Pops the top off the stack.
	 *
	 * @return the top of the stack.
	 * @throws NoSuchElementException if the stack is empty.
	 */

	K pop();

	
Checks whether the stack is empty.
Returns:
true if the stack is empty./** Checks whether the stack is empty.
	 *
	 * @return true if the stack is empty.
	 */

	boolean isEmpty();

	
Peeks at the top of the stack (optional operation).
This default implementation returns peek(0). 
Throws:
NoSuchElementException – if the stack is empty.
Returns:
the top of the stack./** Peeks at the top of the stack (optional operation).
	 *
	 * <p>This default implementation returns {@link #peek(int) peek(0)}.
	 *
	 * @return the top of the stack.
	 * @throws NoSuchElementException if the stack is empty.
	 */

	default K top()  {
		return peek(0);
	}

	
Peeks at an element on the stack (optional operation).
This default implementation just throws an UnsupportedOperationException. 
Params:
i – an index from the stop of the stack (0 represents the top).
Throws:
IndexOutOfBoundsException – if the designated element does not exist..
Returns:
the i-th element on the stack./** Peeks at an element on the stack (optional operation).
	 *
	 * <p>This default implementation just throws an {@link UnsupportedOperationException}.
	 *
	 * @param i an index from the stop of the stack (0 represents the top).
	 * @return the {@code i}-th element on the stack.
	 * @throws IndexOutOfBoundsException if the designated element does not exist..
	 */

	default K peek(int i) {
		throw new UnsupportedOperationException();
	}
}