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
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