RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved poking through strings. (Note that this ends today.)

Task 1: Percentage of Character

You are given a string, $str and a character $char.

Write a script to return the percentage, nearest whole, of given character in the given string.

Two parts to this, then: counting the matching characters, and doing the calculation. Some languages (Ruby, Python, Crystal, Rust) will just give you a count of the matching characters as a function of a string; others allow a filter and count. And in Perl (and Lua) you have to do it the hard way.

use integer;
sub percentageofcharacter($a, $c) {
  my $d = length($a);
  my $n = 0;
  while ($a =~ /$c/g) {
    $n++;
  }
  $n *= 100;
  return ($n + $d / 2) / $d;
}

Most languages have integer variables these days; only JavaScript forces me to use floating point. (I could use BigInts but it would be a pain.)

function percentageofcharacter(a, c) {
    const d = a.length;
    const n = 100 * a.split("").filter(n => n == c).length;
    return Math.floor(n / d + 0.5);
}

Task 2: B After A

You are given a string, $str.

Write a script to return true if there is at least one b, and no a appears after the first b.

In the simple regexp form, this would be matching /^[^b]*b[^a]*$/. But I tried doing without instead. Kotlin:

fun baftera(a: String): Boolean {
    val firstb = a.indexOf('b')
    val lasta = a.lastIndexOf('a')
    if (firstb == -1) {
        return false
    }
    if (lasta == -1) {
        return true
    }
    return lasta < firstb
}

Lua and PostScript don't have a "find last", but one can reverse the string, find first, and then do maths to get the index value.

Full code on github.