# Difference between revisions of "RosettaCode Monty Hall"

Peter gummer (Talk | contribs) (→Eiffel code) |
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==Eiffel code== | ==Eiffel code== | ||

+ | |||

+ | Here's an initial implementation, just to get things started. I just typed this straight into the wiki, so it might not even compile. | ||

+ | |||

+ | Please feel free to edit this in place, I won't be offended. | ||

+ | |||

+ | <e> | ||

+ | class MONTY_HALL | ||

+ | |||

+ | feature | ||

+ | |||

+ | play | ||

+ | local | ||

+ | games: INTEGER | ||

+ | random: RANDOM | ||

+ | doors: ARRAYED_LIST [BOOLEAN] | ||

+ | chosen, shown: INTEGER | ||

+ | stayWins: INTEGER | ||

+ | do | ||

+ | games := 1000000 | ||

+ | create random.make | ||

+ | |||

+ | across 1 |..| games as plays loop | ||

+ | create doors.make_filled (3) -- False is a goat, True is a car | ||

+ | random.forth | ||

+ | doors [random.item \\ 3 + 1] := True -- Put a car behind a random door | ||

+ | |||

+ | random.forth | ||

+ | chosen := random.item \\ 3 + 1 -- Pick a door, any door | ||

+ | |||

+ | from shown := chosen until shown /= chosen and not doors [shown] loop | ||

+ | random.forth | ||

+ | shown := random.item \\ 3 + 1 | ||

+ | end | ||

+ | |||

+ | if doors [chosen] then -- If you would have won by staying, count it | ||

+ | stay_wins := stay_wins + 1 | ||

+ | end | ||

+ | end | ||

+ | |||

+ | out ("Staying wins " + stay_wins + " times.%N") | ||

+ | out ("Switching wins " + games - stay_wins + " times.%N") | ||

+ | end | ||

+ | |||

+ | end | ||

+ | |||

+ | </e> | ||

+ | |||

+ | Note that the implementations in many other languages maintain a separate variable to count the number of switch wins. They calculate whether switching wins at each step via some funky logic that relies on zero-based array indexing, which would be inconvenient in Eiffel. But we don't need to do that at all anyway, because calculating it at each step is completely redundant: we can just do a final subtraction at the end, right? | ||

==Comments== | ==Comments== |

## Revision as of 16:14, 9 August 2012

## Reference

Statement of the Monty Hall problem on RosettaCode: here.

Deadline for adding to RosettaCode page: 31 Aug 2012; submitter:

## Eiffel code

Here's an initial implementation, just to get things started. I just typed this straight into the wiki, so it might not even compile.

Please feel free to edit this in place, I won't be offended.

class MONTY_HALL feature play local games: INTEGER random: RANDOM doors: ARRAYED_LIST [BOOLEAN] chosen, shown: INTEGER stayWins: INTEGER do games := 1000000 create random.make across 1 |..| games as plays loop create doors.make_filled (3) -- False is a goat, True is a car random.forth doors [random.item \\ 3 + 1] := True -- Put a car behind a random door random.forth chosen := random.item \\ 3 + 1 -- Pick a door, any door from shown := chosen until shown /= chosen and not doors [shown] loop random.forth shown := random.item \\ 3 + 1 end if doors [chosen] then -- If you would have won by staying, count it stay_wins := stay_wins + 1 end end out ("Staying wins " + stay_wins + " times.%N") out ("Switching wins " + games - stay_wins + " times.%N") end end

Note that the implementations in many other languages maintain a separate variable to count the number of switch wins. They calculate whether switching wins at each step via some funky logic that relies on zero-based array indexing, which would be inconvenient in Eiffel. But we don't need to do that at all anyway, because calculating it at each step is completely redundant: we can just do a final subtraction at the end, right?