function findIndex(array, element) {
  let firstIndex = 0;
  let lastIndex = array.length - 1;
  let indexOfElement;

  while (firstIndex <= lastIndex) {
    const middleIndex = Math.floor((firstIndex + lastIndex) / 2);
    if (array[middleIndex] === element) return middleIndex;

    if (array[middleIndex] > element) {
      lastIndex = middleIndex - 1;
      indexOfElement = middleIndex;
    } else {
      firstIndex = middleIndex + 1;
      indexOfElement = firstIndex;
    }
  }

  return indexOfElement;
}

function activityNotifications(expenditure, d) {
  let notifications = 0;
  const sorted = expenditure.slice(0, d).sort((a, b) => a - b);

  for (let i = d; i < expenditure.length; i++) {
    const median =
      d % 2 === 1
        ? sorted[Math.floor(d / 2)]
        : (sorted[d / 2 - 1] + sorted[d / 2]) / 2;
    if (expenditure[i] >= 2 * median) notifications += 1;

    sorted.splice(findIndex(sorted, expenditure[i - d]), 1);
    sorted.splice(findIndex(sorted, expenditure[i]), 0, expenditure[i]);
  }

  return notifications;
}