Department numbers: Difference between revisions

===Using a constraint solver===

A problem this trivial is amenable to brute-force solutions such as the above, but it is a good example of the type of problem for which a constraint solver can be useful. This is how one could solve it using the `python-constraint` library:

{{libheader|python-constraint}}

<syntaxhighlight lang="python">import constraint

depts = [ 'police', 'sanitation', 'fire' ]

p = constraint.Problem()

for var in depts:

p.addVariable(var, range(1,8))

p.addConstraint(constraint.AllDifferentConstraint())

p.addConstraint(lambda *vars: sum(vars)==12, depts)

p.addConstraint(lambda p: p%2==0, ['police'])

for s in p.getSolutions():

print(s)</syntaxhighlight>

{{Out}}

<pre>{'police': 6, 'fire': 5, 'sanitation': 1}

{'police': 6, 'fire': 4, 'sanitation': 2}

{'police': 6, 'fire': 2, 'sanitation': 4}

{'police': 6, 'fire': 1, 'sanitation': 5}

{'police': 4, 'fire': 6, 'sanitation': 2}

{'police': 4, 'fire': 7, 'sanitation': 1}

{'police': 4, 'fire': 5, 'sanitation': 3}

{'police': 4, 'fire': 3, 'sanitation': 5}

{'police': 4, 'fire': 2, 'sanitation': 6}

{'police': 4, 'fire': 1, 'sanitation': 7}

{'police': 2, 'fire': 4, 'sanitation': 6}

{'police': 2, 'fire': 6, 'sanitation': 4}

{'police': 2, 'fire': 7, 'sanitation': 3}

{'police': 2, 'fire': 3, 'sanitation': 7}</pre>