RogerBW's Blog

The Weekly Challenge 231: Max Citizens 27 August 2023

I’ve been doing the Weekly Challenges. The latest involved various list processing. (Note that this ends today.)

Task 1: Min Max

You are given an array of distinct integers.

Write a script to find all elements that is neither minimum nor maximum. Return -1 if you can't.

So basically a list filter. I calculate and cache min and max values, then filter. This is probably cheaper than sorting the list then topping and tailing, and anyway that would destroy the order.


fun notminmax(a: List<Int>): List<Int> {
    val mn = a.minOrNull()!!
    val mx = a.maxOrNull()!!
    return a.filter {it != mn && it != mx}.toList()

Task 2: Senior Citizens

You are given a list of passenger details in the form "9999999999A1122", where 9 denotes the phone number, A the sex, 1 the age and 2 the seat number.

Write a script to return the count of all senior citizens (age >= 60).

We could decode the whole thing, but all we need to look at is character 11; 6+ is a hit.

This can be written verbosely (Raku):

sub seniorcitizens(@a) {
    my $p = 0;
    for @a -> $n {
        my $c = substr($n, 11, 1);
        if ($c ge '6') {
    return $p;

or with no variables at all (PostScript):

/seniorcitizens {
    0 exch
        11 get 16#36 ge {
            1 add
        } if
    } forall
} bind def

Or compactly (Ruby):

def seniorcitizens(a)
  return a.count {|x| x[11] >= "6"}

Full code on github.

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