Sunday Times Teaser 2646 – Monday Birthdays

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   brian gladman permalink

   Sundaay Times Teaser 2646

   Python

   from collections import defaultdict from datetime import date days = ( 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday' ) # Starting at the date 'born', count the number of birthdays # falling on a Monday in the next hundred years def count(born, d): cnt = 0 for year in range(born.year, born.year + 101): try: if date(year, born.month, born.day).weekday() == 0: cnt += 1 except ValueError: pass # record the count indexed on birth month and weekday d[born.month][born.weekday()] = cnt # counts for Harry and Peter indexed on birth month and weekday harry = defaultdict(lambda: defaultdict(list)) peter = defaultdict(lambda: defaultdict(list)) # look at all dates in 2012 for day_nbr in range(date(2012, 1, 1).toordinal(), date(2013, 1, 1).toordinal()): now = date.fromordinal(day_nbr) # compile the counts for Harry and Peter count(now.replace(year = now.year - 100), harry) count(now, peter) # look for months and weekdays for which Peter's count # is two less than Harry's sol = set() for month in range(1, 13): for weekday in range(7): if harry[month][weekday] == peter[month][weekday] + 2: sol |= set((weekday,)) print('Both Harry and Peter were born on a {:s}.'.format(days[min(sol)]))

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   from collections import defaultdict from datetime import date   days = ( 'Monday', 'Tuesday', 'Wednesday', 'Thursday',          'Friday', 'Saturday', 'Sunday' )   # Starting at the date 'born', count the number of birthdays # falling on a Monday in the next hundred years def count(born, d):   cnt = 0   for year in range(born.year, born.year + 101):     try:       if date(year, born.month, born.day).weekday() == 0:         cnt += 1     except ValueError:       pass   # record the count indexed on birth month and weekday   d[born.month][born.weekday()] = cnt   # counts for Harry and Peter indexed on birth month and weekday harry = defaultdict(lambda: defaultdict(list)) peter = defaultdict(lambda: defaultdict(list))   # look at all dates in 2012 for day_nbr in range(date(2012, 1, 1).toordinal(),                      date(2013, 1, 1).toordinal()):   now = date.fromordinal(day_nbr)   # compile the counts for Harry and Peter   count(now.replace(year = now.year - 100), harry)   count(now, peter)   # look for months and weekdays for which Peter's count # is two less than Harry's sol = set() for month in range(1, 13):   for weekday in range(7):     if harry[month][weekday] == peter[month][weekday] + 2:       sol |= set((weekday,)) print('Both Harry and Peter were born on a {:s}.'.format(days[min(sol)]))

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