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JavaScript Searching and Sorting Algorithm: Find the highest index at which a value should be inserted into an array in order to maintain its sort order, based on a provided iterator function

JavaScript Searching and Sorting Algorithm: Exercise-17 with Solution

Write a JavaScript program to find the highest index at which a value should be inserted into an array in order to maintain its sort order, based on a provided iterator function.

Sample Solution:

JavaScript Code:

const sortedLastIndexBy = (arr, n, fn) => {
  const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
  const val = fn(n);
  const index = arr
    .map(fn)
    .reverse()
    .findIndex(el => (isDescending ? val <= el : val >= el));
  return index === -1 ? 0 : arr.length - index;
};

console.log(sortedLastIndexBy([{ x: 4 }, { x: 5 }], { x: 4 }, o => o.x));

Sample Output:

1

Flowchart:

JavaScript Searching and Sorting Algorithm Exercises: Find the highest index at which a value should be inserted into an array in order to maintain its sort order, based on a provided iterator function.

Live Demo:

See the Pen javascript-common-editor by w3resource (@w3resource) on CodePen.


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JavaScript: Tips of the Day

How to insert an item into an array at a specific index (JavaScript)?

What you want is the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert). In this example we will create an array and add an element to it into index 2:

var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";

console.log(arr.join());
arr.splice(2, 0, "Lene");
console.log(arr.join());

Ref: https://bit.ly/2BXbp04