Kebab file names

snippets/sorted-last-index.md

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+---
+title: Last insertion index in sorted array
+tags: array
+cover: rocky-beach-3
+firstSeen: 2018-01-24T13:16:47+02:00
+lastUpdated: 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.
+
+```js
+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;
+};
+```
+
+```js
+sortedLastIndex([10, 20, 30, 30, 40], 30); // 4
+```