How to Generate Non-Repeating Random Numbers in JavaScript without Recursion

Generating Non-Repeating Random Numbers in JavaScript

The goal of this task is to generate a sequence of random numbers within a specified range that do not repeat. One approach involves checking each generated number against a list of previously created numbers. However, this method can lead to a "RangeError" due to excessive recursion.

A better solution is to generate a random permutation of the desired numbers upfront. This can be achieved using various techniques:

Random Permutation

<code class="javascript">var nums = [1,2,3,4,5,6,7,8,9,10],
    ranNums = [],
    i = nums.length,
    j = 0;

while (i--) {
    j = Math.floor(Math.random() * (i+1));
    ranNums.push(nums[j]);
    nums.splice(j,1);
}</code>

This algorithm generates a random ordering of the numbers in nums. If you want to restrict the range or specify even numbers, you can modify nums accordingly.

Fisher-Yates Shuffle

<code class="javascript">function shuffle(array) {
    var i = array.length,
        j = 0,
        temp;

    while (i--) {

        j = Math.floor(Math.random() * (i+1));

        // swap randomly chosen element with current element
        temp = array[i];
        array[i] = array[j];
        array[j] = temp;

    }

    return array;
}

var ranNums = shuffle([1,2,3,4,5,6,7,8,9,10]);</code>

The Fisher-Yates Shuffle is a more efficient alternative to the random permutation method, as it avoids the use of costly array operations.

Generators

<code class="javascript">function* shuffle(array) {

    var i = array.length;

    while (i--) {
        yield array.splice(Math.floor(Math.random() * (i+1)), 1)[0];
    }

}</code>

Generators offer an even more dynamic option. By utilizing the yield and next methods, you can access the shuffled numbers on demand without pre-generating the entire sequence.

This approach is especially useful in cases where you need a large number of random numbers and want to avoid holding them all in memory at once.

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