30-seconds-of-code/snippets/sortedLastIndex.md

title, tags, expertise, cover, firstSeen, lastUpdated

title	tags	expertise	cover	firstSeen	lastUpdated
Last insertion index in sorted array	array	intermediate	blog_images/rocky-beach-3.jpg	2018-01-24T13:16:47+02:00	2020-10-22T20:24:30+03:00

Finds the highest index at which a value should be inserted into an array in order to maintain its sort order.

• Loosely check if the array is sorted in descending order.
• Use Array.prototype.reverse() and Array.prototype.findIndex() to find the appropriate last index where the element should be inserted.

const sortedLastIndex = (arr, n) => {
  const isDescending = arr[0] > arr[arr.length - 1];
  const index = arr
    .reverse()
    .findIndex(el => (isDescending ? n <= el : n >= el));
  return index === -1 ? 0 : arr.length - index;
};

sortedLastIndex([10, 20, 30, 30, 40], 30); // 4