JavaScript: Find the number of inversions of a specified array of integers

Last update on May 30 2022 09:58:55 (UTC/GMT +8 hours)

JavaScript Basic: Exercise-102 with Solution

Write a JavaScript program to find the number of inversions of a given array of integers.

Note: Two elements of the array a stored at positions i and j form an inversion if a[i] > a[j] and i < j.

Sample Solution:

HTML Code:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title> Find the number of inversions of a specified array of integers</title>
</head>
<body>

</body>
</html>

JavaScript Code:

function number_of_InversionsNaive(arr) {
    var ctr = 0;
    for (var i = 0; i < arr.length; i++) {
        for (var j = i + 1; j < arr.length; j++) {
            if (arr[i] > arr[j]) 
              ctr++;
        }
    }
    return ctr;
}

console.log(number_of_InversionsNaive([0, 3, 2, 5, 9]));   
console.log(number_of_InversionsNaive([1, 5, 4, 3]));   
console.log(number_of_InversionsNaive([10, 30, 20, -10]));

Sample Output:

1
3
4

Flowchart:

ES6 Version:

function number_of_InversionsNaive(arr) {
    let ctr = 0;
    for (let i = 0; i < arr.length; i++) {
        for (let j = i + 1; j < arr.length; j++) {
            if (arr[i] > arr[j]) 
              ctr++;
        }
    }
    return ctr;
}

console.log(number_of_InversionsNaive([0, 3, 2, 5, 9]));   
console.log(number_of_InversionsNaive([1, 5, 4, 3]));   
console.log(number_of_InversionsNaive([10, 30, 20, -10]));

Live Demo:

See the Pen javascript-basic-exercise-102 by w3resource (@w3resource) on CodePen.

Contribute your code and comments through Disqus.

Previous: Write a JavaScript program to check whether a given string contains only Latin letters and no two uppercase and no two lowercase letters are in adjacent positions.
Next: Write a JavaScript program to find the maximum number from a given positive integer by deleting exactly one digit of the given number.

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