22 lines
669 B
Markdown
22 lines
669 B
Markdown
---
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title: sortedLastIndex
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tags: array,math,intermediate
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---
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Returns the highest index at which value should be inserted into array in order to maintain its sort order.
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- Check if the array is sorted in descending order (loosely).
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- Use `Array.prototype.reverse()` and `Array.prototype.findIndex()` to find the appropriate last index where the element should be inserted.
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```js
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const sortedLastIndex = (arr, n) => {
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const isDescending = arr[0] > arr[arr.length - 1];
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const index = arr.reverse().findIndex(el => (isDescending ? n <= el : n >= el));
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return index === -1 ? 0 : arr.length - index;
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};
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```
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```js
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sortedLastIndex([10, 20, 30, 30, 40], 30); // 4
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```
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