Generate a Random Permutation of 1 to n in JavaScript

In programming, creating a random permutation of numbers from 1 to n is a common task. A random permutation means randomly rearranging the elements that make up a permutation.

Below are the methods to generate a random permutation of 1 to n in JavaScript:

Fisher-Yates (Knuth) Algorithm

The Knuth shuffle, also called the Fisher-Yates algorithm, is a popular method to generate random permutations. It replaces each element in the array with a previously chosen element at random as it iterates through the array from the last to the first element. This ensures an impartial and effective shuffle.

Example: The function generates a random permutation of numbers from 1 to n using the Fisher-Yates (Knuth) Algorithm.

function generateRandomPermutation(n) {
  let permutation = Array
    .from({ length: n }, (_, i) => i + 1);

  for (let i = n - 1; i > 0; i--) {
    const j = Math
      .floor(Math.random() * (i + 1));
    [permutation[i], permutation[j]]
      =
      [permutation[j], permutation[i]];
  }

  return permutation;
}

console.log("Fisher-Yates (Knuth) Algorithm:");
console.log(generateRandomPermutation(5));

Fisher-Yates (Knuth) Algorithm:
[ 1, 3, 2, 5, 4 ]

Using Built-in Functions

It is also possible to create a random permutation in JavaScript by combining a random number generator with built-in functions like Array.from() and Array.prototype.sort().

Example: The function generates a random permutation of numbers from 1 to n using built-in functions.

function generateRandomPermutation(n) {
    let permutation = Array
        .from({ length: n }, (_, i) => i + 1);

    permutation
        .sort(() => Math.random() - 0.5);

    return permutation;
}

console.log("Using Built-in Functions:");
console.log(generateRandomPermutation(5));

Using Built-in Functions:
[ 3, 1, 4, 2, 5 ]