Method peek

stacks/triple-stack.js:42–50

(stack)

  }

  peek(stack) {
    let length = this._getLength(stack),
      value;
    if (length > 0) {
      let idx = (length - 1) * 3 + stack - 1;
      value = this._array[idx];
    }
    return value;
  }

  isEmpty(stack) {
    return this._getLength(stack) === 0;