// I just did this method to not use reduce, concat or any kind of special method from JS and trying to have the
// cheapest complexity.

function flattenArray(array) {
    let i = 0;
    while (i != array.length) {
        let valueOrArray = array[i];
        if (! Array.isArray(valueOrArray)) {
            i++;
        } else {
            array.splice(i, 1, ...valueOrArray);
        }
    }
    return array;
}

function test_flatten_array(){
    let arr1 = [[1,3,[99]],41];
    let arr2 = [1,[9,[5,[3],52,],8],2];

    console.log('Flattened array 1:', flattenArray(arr1));
    console.log('Flattened array 2:', flattenArray(arr2));
}

test_flatten_array();