RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved string searching. (Note that this ends today.)

Task 1: Count Vowel

You are given a string.

Write a script to return all possible vowel substrings in the given string. A vowel substring is a substring that only consists of vowels and has all five vowels present in it.

With the slight complication that we want the shortest possible: given a fragment "aeiouu" we return "aeiou" and not also "aeiouu". In Rust:

fn countvowel(a0: &str) -> Vec<String> {

Break the string into a list of characters.

    let a = a0.chars().collect::<Vec<_>>();

Initialise the output list.

    let mut found = Vec::new();

Starting length value, which we may reset later.

    let mut l = a.len();

Loop from (length - 5) down to 0 for a starting position.

    for start in (0..=l - 5).rev() {

Loop from 5 characters after that to the "end of the string" (see later).

        'END: for eend in start + 5..=l {

Extract this substring, and make a set of its characters.

            let mut sample = a[start..eend].iter().collect::<HashSet<_>>();

If any of the vowels is not present in the sample, break out of this loop and go to the next (earlier) starting position.

            for c in ['a', 'e', 'i', 'o', 'u'] {
                if !sample.contains(&c) {
                    continue 'END;
                }
                sample.remove(&c);
            }

Otherwise, if there weren't any other characters (i.e. a successful match), note this substring, and then reset the "end of the string" to one character before this substring ended. That is to say, we make sure the last character in this substring is no longer available for comparison. Then jump to the next (earlier) starting position.

            if sample.len() == 0 {
                found.push(a[start..eend].iter().collect::<String>());
                l = eend - 1;
                break;
            }
        }
    }

Sort the results, for convenience of testing. (Can't use a Set as there may be duplicates.)

    found.sort();
    found
}

Task 2: Largest Same-digits Number

You are given a string containing 0-9 digits only.

Write a script to return the largest number with all digits the same in the given string.

Fortunately there's a nice deterministic way to generate all possibilities, so I just search exhaustively. In Perl:

sub largestsamedigitsnumber($a) {

Count down from the longest possible string.

  foreach my $l (reverse (1 .. length($a))) {

Within that length, count down digits. (So a three-character string will be searched for 999, 888, 777, [...], 222, 111, 99, 88, 77. [...])

    foreach my $n (reverse (1 .. 9)) {

Build a search string.

      my $test = $n x $l;

If it's in the input, return its numerical value.

      if (index($a, $test) > -1) {
        return 0 + $test;
      }
    }
  }

If we didn't find anything, return zero. (In the special case of a string with only zeroes.)

  0;
}

Full code on codeberg.