My Rust approach:

fn countingSort(arr: &[i32]) -> Vec { let mut my_vec: Vec = vec![0; 100];

for var in arr {
    if let Some(x) = my_vec.get_mut(*var as usize) {
        *x += 1;
    }
}

my_vec

} `

For those who stumbled into the same issue as me, make sure that you understand what a frequency array is first, and the proper way to create one, otherwise you will bang your head into a wall over this problem. I ran into issues because I didn't realize it is supposed to be size 100, for every single case. I was making it the same size as the size as the input array.

Python solution

def countingSort(arr):
    freq = [0] * 100
    
    for n in arr:
        freq[n] += 1
        
    return freq

I feel like this challenge is a lot easier than the challenges suggested before it, and should probably be one of the first ones given.