/*
Stack, array implementation
http://www.cs.usfca.edu/~galles/visualization/StackArray.html
*/
class Stack {
  constructor() {
    this._stack = [];
    this._index = -1;
  }
  push(value) {
    this._index++;
    this._stack[this._index] = value;
  }
  pop() {
    const resultingArray = this._stack.splice(this._index, 1);
    this._index--;
    return resultingArray[0];
  }
}