RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved light parsing and tax bracket calculations. (Note that this ends today.)

Task 1: Increment Decrement

You are given a list of operations.

Write a script to return the final value after performing the given operations in order. The initial value is always 0.

Possible Operations: ++x or x++: increment by 1 --x or x--: decrement by 1

From which I observe that the parsing can be reduced to a single question: "is the second character a '+'?" Or, for the regex-heavy languages, "does the string contain a '+'?" In Raku:

sub incrementdecrement(@operations) {
    my $p = 0;
    for @operations -> $s {
        if ($s ~~ /\+/) {
            $p++;
        } else {
            $p--;
        }
    }
    $p;
}

Meanwhile in PostScript:

/incrementdecrement {
    0 exch
    {
        1 get 43 eq {
            1 add
        } {
            1 sub
        } ifelse
    } forall
} bind def

Task 2: Tax Amount

You are given an income amount and tax brackets.

Write a script to calculate the total tax amount.

The brackets are specified as an upper bound and a rate, with the lower bound being the upper bound of the previous bracket (or zero).

Python:

def taxamount(income, brackets):

Set up the tax accumulator, and the upper bound of the previous bracket.

  tax = 0
  lastbracket = 0

Iterate over brackets.

  for bracket in brackets:

If this bracket is at all relevant to us,

    if income > lastbracket:

The tax contribution is the lower of total income and upper bound, minus the lower bound, multiplied by the tax rate/

      tax += (min(income, bracket[0]) - lastbracket) * bracket[1]

If the lower bound was more than our income, since the brackets are in order, we can bail out here.

    else:
      break

Set our upper bound as the lower bound of the next bracket.

    lastbracket = bracket[0]

For languages which support it, I've been doing all this in integers, but I have to return the result as a float.

  return tax / 100

Full code on github.