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

title, tags

title	tags
sortedLastIndex	array,math,intermediate

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

• Check if the array is sorted in descending order (loosely).
• 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