Billing Period

May 18, 2018

I’m not sure of the origin of today’s exercise, but given the contrived nature of the calculation, I suspect it’s a programming exercise for beginning programming students:

Our merchants receive “weekly” invoices, following these rules:

  • Each Saturday marks the beginning of a new billing period.
  • Each 1st of a month marks the begining of a new billing period.
  • Within a year, billing periods are numbered consecutively, starting with billing period 1 on January 1st.

Thus, a billing period can be referenced by a year and period number.

Your task is to write a program that calculates the billing period for a given date. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

Pages: 1 2

Posted by programmingpraxis
Filed in Exercises
5 Comments »

5 Responses to “Billing Period”

  1. Steve said
    May 18, 2018 at 2:29 PM

    Mumps/Cache version

    billingperiod ;
         q
         ;
go(dt)   ;
         n adt,dti,dts,dtsi,i,period
         s dti=$zdh(dt),dts="01/01/"_$p(dt,"/",3),dtsi=$zdh(dts)
         s period=0
         f i=dtsi:1:dti d
         . s adt=$zd(i)
         . i $p(adt,"/",2)="01" s period=period+1
         . e  i i#7=2 s period=period+1 ; Saturday
         q period
 
---

f dt="01/01/2018","01/05/2018","01/06/2018","01/12/2018","01/13/2018","01/19/2018","01/20/2018","01/26/2018","01/27/2018","01/31/2018","02/01/2018","08/31/2018","09/01/2018","09/02/2018" w !,dt," -- ",$$go^billingperiod(dt)

01/01/2018 -- 1
01/05/2018 -- 1
01/06/2018 -- 2
01/12/2018 -- 2
01/13/2018 -- 3
01/19/2018 -- 3
01/20/2018 -- 4
01/26/2018 -- 4
01/27/2018 -- 5
01/31/2018 -- 5
02/01/2018 -- 6
08/31/2018 -- 42
09/01/2018 -- 43
09/02/2018 -- 43
  2. WWW.ХХХ.ZСVIW.ХУZ said
    May 18, 2018 at 2:58 PM

    What ?

  3. Steve said
    May 18, 2018 at 3:43 PM

    Mumps/Cache version, with comments and expanded commands, etc

    billingperiod ;
         quit
         ;
go(dt)   ;
         new adt,dti,dts,dtsi,i,period ; initialize variables
         set dti=$zdh(dt),dts="01/01/"_$p(dt,"/",3),dtsi=$zdh(dts) ; get internal date,external Jan 1 date,internal Jan 1 date
         set period=0 ; initialize period count
         for i=dtsi:1:dti do  ; loop through dates from Jan 1 to target date
         . set adt=$zd(i) ; get external form of date from loop
         . if $piece(adt,"/",2)="01" set period=period+1 ; if loop date is first of the month, increment counter
         . else  if i#7=2 set period=period+1 ; Otherwise, if loop date is Saturday, increment counter
         q period
 
---
; For each of these dates, print date and calculated period  ($$go^billingperiod is the called function)
for dt="01/01/2018","01/05/2018","01/06/2018","01/12/2018","01/13/2018","01/19/2018","01/20/2018","01/26/2018","01/27/2018","01/31/2018","02/01/2018","08/31/2018","09/01/2018","09/02/2018" write !,dt," -- ",$$go^billingperiod(dt)

01/01/2018 -- 1
01/05/2018 -- 1
01/06/2018 -- 2
01/12/2018 -- 2
01/13/2018 -- 3
01/19/2018 -- 3
01/20/2018 -- 4
01/26/2018 -- 4
01/27/2018 -- 5
01/31/2018 -- 5
02/01/2018 -- 6
08/31/2018 -- 42
09/01/2018 -- 43
09/02/2018 -- 43
  4. Daniel said
    May 20, 2018 at 6:06 AM

    Here’s a solution in C.

    #include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

int calc_julian(int year, int month, int day) {
  int m1 = (month-14)/12;
  int y1 = year+4800;
  int julian = 1461*(y1+m1)/4;
  julian += (367*(month-2-12*m1))/12;
  julian += (-3*((y1+m1+100)/100))/4;
  julian += day-32075;
  return julian;
}

int calc_billing_period(int year, int month, int day) {
  int billing_period = 0;
  int start = calc_julian(year, 1, 1);
  int end = calc_julian(year, month, day);
  // Add the number of full weeks (each of these includes a Saturday).
  int n_days = end - start + 1;
  int n_full_weeks = n_days / 7;
  billing_period += n_full_weeks;
  // Add 1 if there is a Saturday in the partial week.
  int remainder = n_days % 7;
  int start_day = start % 7;
  bool another_saturday = (remainder > 0)
    && (start_day != 6)
    && (start_day + remainder - 1 >= 5);
  billing_period += another_saturday;
  // Add the months that didn't start on Saturday.
  for (int i = 1; i <= month; ++i) {
    billing_period += (calc_julian(year, i, 1) % 7) != 5;
  }
  return billing_period;
}

int main(int argc, char* argv[]) {
  if (argc != 4) {
    fprintf(stderr, "Usage: %s <YEAR> <MONTH> <DAY>\n", argv[0]);
    return EXIT_FAILURE;
  }
  int year = atoi(argv[1]);
  int month = atoi(argv[2]);
  int day = atoi(argv[3]);
  int billing_period = calc_billing_period(year, month, day);
  printf("%d\n", billing_period);
  return EXIT_SUCCESS;
}

    Example:

    $ ./billing_period 2018 5 18
24
  5. V said
    May 21, 2018 at 4:57 AM

    In Ruby.

    require 'date'

def billing_period(date_str)
  target_date  = Date.parse(date_str)
  jan_first    = Date.new(target_date.year, 1,1)
  (jan_first..target_date).reduce(0) do |period, date|
    date.day == 1 || date.saturday? ? period + 1 : period
  end
end

[
  '2018-01-01',
  '2018-01-03',
  '2018-01-06',
  '2018-01-10',
  '2018-01-26',
  '2018-02-01',
  '2018-05-18'
].each do |date|
  puts "#{date} -> #{billing_period(date)}"
end

    Output:

    2018-01-01 -> 1
    2018-01-03 -> 1
    2018-01-06 -> 2
    2018-01-10 -> 2
    2018-01-26 -> 4
    2018-02-01 -> 6
    2018-05-18 -> 24

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