Code for 2018-01-26 riddler classic; https://fivethirtyeight.com/features/how-often-does-the-senate-vote-in-palindromes/

color.py

#!/usr/bin/env python3

import argparse
import sys
import collections

def main():
  areas = { 'a' : 12,
            'b' : 12,
            'c' : 12,
            'd' : 6,
            'e' : 3,
            'f' : 6,
            'g' : 21,
            'h' : 6,
            'i' : 12,
            'j' : 3,
            'k' : 9,
            'l' : 6,
            'm' : 12,
            'n' : 24 }
  adjacencies = { 'a' : 'bcd',
                  'b' : 'ac',
                  'c' : 'abfeg',
                  'd' : 'agm',
                  'e' : 'cfg',
                  'f' : 'ec',
                  'g' : 'cedh',
                  'h' : 'mgi',
                  'i' : 'hl',
                  'j' : 'nk',
                  'k' : 'jl',
                  'l' : 'mki',
                  'm' : 'dhln',
                  'n' : 'mj' }

  def pick_colors(regions, colors):
    if not regions:
      totals = collections.defaultdict(int)
      for r, c in colors.items():
        totals[c] += areas[r]
      if all(v == 36 for v in totals.values()):
        print(colors)
    else:
      r = regions[0]
      for c in (x for x in range(4)
                if all(colors.get(n) != x for n in adjacencies[r])):
        colors[r] = c
        pick_colors(regions[1:], colors)
      del colors[r]

  pick_colors('defghijklmn',
              { 'a' : 0, 'b' : 1, 'c' : 2 })  # remove symmetries

if __name__ == "__main__":
  sys.exit(main())