数据结构与算法之Stack（栈）——重新实现

      之前发过一篇stack的实现，是采用dart内置的List类并固定长度数组实现的。这里重新实现一版，重复利用List类内置特性和方法。实现更为简洁。

class Stack<E> {
  final List<E> _stack;

  Stack() : _stack = <E>[];

  bool get isEmpty => _stack.isEmpty;
  bool get isNotEmpty => _stack.isNotEmpty;
  int get size => _stack.length;

  Iterable<E> get content => _stack.reversed;

  void push(E e) => _stack.add(e);

  E pop() {
    if (_stack.isEmpty) throw StackEmptyException;
    return _stack.removeLast();
  }

  E get top {
    if (_stack.isEmpty) throw StackEmptyException;
    return _stack.last;
  }
}

class StackEmptyException implements Exception {
  const StackEmptyException();
  String toString() => 'StackEmptyException';
}