RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved character repetition and a basic string parse. (Note that this ends today.)

Task 1: Twice Appearance

You are given a string, $str, containing lowercase English letters only.

Write a script to print the first letter that appears twice.

The way to do this that seemed most obvioius to me was to iterate with a set: if the character is already in the set, return it, otherwise put it in the set.

One could add error handling in the case that no character is repeated, but that's outside the problem scope.

sub twiceappearance($a) {

Construct the set.

    my %m = SetHash.new;

For each character,

    for $a.comb -> $c {

If it's in the set,

        if (%m{$c}:exists) {

Return it.

            return $c
        }

Otherwise add it to the set.

        %m{$c}++;
    }

We should never get here but in languages with return types this is needed.

    return 'x';
}

Task 2: Count Asterisks

You are given a string, $str, where every two consecutive vertical bars are grouped into a pair.

Write a script to return the number of asterisks, *, excluding any between each pair of vertical bars.

One could probably do this with proper parsing, but the quick way seemed to be to iterate characters again: a | toggles the active flag (which begins as true), and a * adds to the count if the active flag is true.

Rust:

fn countasterisks(a: &str) -> u32 {

Set output value and active flag.

    let mut out = 0;
    let mut active = true;

For each character,

    for c in a.chars() {
        match c {

If it's |, toggle active flag.

            '|' => active = !active,

If it's * and active is true, add one to the output.

            '*' => {
                if active {
                    out += 1
                }
            }
            _ => {}
        }
    }
    out
}

Full code on github.