RogerBW's Blog

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

Task 1: Unique Number

You are given an array of integers, @ints, where every elements appears more than once except one element.

Write a script to find the one element that appears exactly one time.

Which means "stuff the list into a hash of entries and counts", first.

PostScript:

/uniquenumber {
    0 dict begin

Build the counter.

    /c 0 dict def
    {
        /n exch def
        c n c n 0 dget 1 add put
    } forall

Then search the hash to find the key where the value is 1.

    -1
    c keys {
        /n exch def
        c n 0 dget 1 eq {
            pop n
            exit
        } if
    } forall
    end
} bind def

Task 2: Digit Count Value

You are given an array of positive integers, @ints.

Write a script to return true if for every index i in the range 0 ≤ i < size of array, the digit i occurs exactly the $ints[$i] times in the given array otherwise return false.

Which wants another counter.

Raku:

sub digitcountvalue(@a) {

Set up the counter.

  my %c;
  @a.map({%c{$_}++});

For each index value:

  for 0 .. @a.end -> $ix {

If the value at that point in the list doesn't equal the count of that value, bail out with false.

    if (@a[$ix] != (%c{$ix} || 0)) {
      return False;
    }
  }

If everything passed, return true.

  return True;
}

Full code on github.