JavaScript Searching and Sorting Algorithm: Check if a numeric array is sorted or not

Last update on May 30 2022 10:06:24 (UTC/GMT +8 hours)

JavaScript Searching and Sorting Algorithm: Exercise-24 with Solution

Write a JavaScript program to check if a numeric array is sorted or not.

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.

Sample Solution:

JavaScript Code:

const isSorted = arr => {
  if (arr.length <= 1) return 0;
  const direction = arr[1] - arr[0];
  for (let i = 2; i < arr.length; i++) {
    if ((arr[i] - arr[i - 1]) * direction < 0) return 0;
  }
  return Math.sign(direction);
};
console.log(isSorted([0, 1, 2, 2]));
console.log(isSorted([4, 3, 2]));
console.log(isSorted([4, 3, 5]));
console.log(isSorted([4]));

Sample Output:

Flowchart:

JavaScript Searching and Sorting Algorithm Exercises: Check if a numeric array is sorted or not.

Live Demo:

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

Improve this sample solution and post your code through Disqus

Previous: 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.
Next: Searching and sorting Algorithm Exercises Home Page.

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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