27 lines
780 B
Markdown
27 lines
780 B
Markdown
---
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title: Last insertion index in sorted array
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tags: array
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cover: rocky-beach-3
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firstSeen: 2018-01-24T13:16:47+02:00
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lastUpdated: 2020-10-22T20:24:30+03:00
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---
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Finds the highest index at which a value should be inserted into an array in order to maintain its sort order.
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- Loosely check if the array is sorted in descending order.
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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
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.reverse()
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.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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