RogerBW's Blog

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

Task 1: Binary Date

You are given a date in the format YYYY-MM-DD.

Write a script to convert it into binary date.

This comes apart into:

1. break the input string by dashes into a list of decimal strings
2. convert each decimal string to a binary string
3. join those binary strings with dashes

The obvious way to do step 2, of course, is to parse the decimal strings into numeric values, then write those out as binary.

Some languages make this a one-liner, like Raku:

sub binarydate($a) {
  $a.split('-').map({sprintf('%b', $_)}).join('-');
}

Some need an explcit binary formatter, like Typst:

#let inttobins(n) = {
  if n == 0 {
    "0"
  } else {
    let d = ()
    let m = n
    while m > 0 {
      if m.bit-and(1) == 1 {
        d.insert(0, "1")
      } else {
        d.insert(0, "0")
      }
      m = calc.quo(m, 2)
    }
    d.join("")
  }
}

#let binarydate(a) = {
  a.split("-").map(n => inttobins(int(n))).join("-")
}

Task 2: Odd Letters

You are given a string.

Write a script to find out if each letter in the given string appeared odd number of times.

I've done enough problems where a counter, i.e. a map of values to their frequency of occurrence, is needed (and in Rust I can use the counter crate to do this directly) that I've developed library functions for generating them automatically (where it's more than trivial). Then it's just a matter of testing the values, ideally with an all operator where it's available. Crystal:

def counterify(a)
  cc = Hash(Char, Int32).new(default_value: 0)
  a.each do |x|
    cc[x] += 1
  end
  return cc
end

def oddletters(a)
  c = counterify(a.chars)
  c.values.all? { |v| v % 2 == 1 }
end

Full code on github.