RosettaCode Monty Hall - Revision history

Marco2357 at 08:27, 3 October 2012

2012-10-03T08:27:26Z

← Older revision		Revision as of 08:27, 3 October 2012
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	[[Category:Flash Code ]]		[[Category:Flash Code ]]

	'''[[RosettaCode]] Overview'''		'''-> [[RosettaCode]] Overview'''

	==Reference==		==Reference==

Marco2357 at 08:27, 3 October 2012

2012-10-03T08:27:12Z

← Older revision		Revision as of 08:27, 3 October 2012
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	[[Category:Rosetta Code]]		[[Category:Rosetta Code]]
	[[Category:Flash Code ]]		[[Category:Flash Code ]]

			'''[[RosettaCode]] Overview'''

	==Reference==		==Reference==

Peter gummer: /* Eiffel code */

2012-08-12T02:40:09Z

Eiffel code

← Older revision		Revision as of 02:40, 12 August 2012
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	Staying wins 333504 times.		Staying wins 333504 times.

	Switching wins 666496 times.		Switching wins 666496 times.

Peter gummer: Monty Hall implementation that compiles and runs

2012-08-12T02:38:06Z

Monty Hall implementation that compiles and runs

← Older revision		Revision as of 02:38, 12 August 2012
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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.~~		Here's a candidate implementation. This compiles and runs, producing output similar to this:

	~~Please feel free to edit this in place, I won't be offended~~.		Staying wins 333504 times.
			Switching wins 666496 times.

	<e>		<e>
	class MONTY_HALL		class
			MONTY_HALL

	feature		create
			make

			feature {NONE} -- Initialization

			make
			local
			games_count: INTEGER
			do
			create random_generator.make
			games_count := 1000000

			across 1 \|..\| games_count as game loop
			play
			end

			print ("Staying wins " + staying_wins.out + " times.%N")
			print ("Switching wins " + (games_count - staying_wins).out + " times.%N")
			end

			feature -- Commands

	play		play
	local		local
	~~games: INTEGER~~
	~~random: RANDOM~~
	doors: ARRAYED_LIST [BOOLEAN]		doors: ARRAYED_LIST [BOOLEAN]
	chosen, shown: INTEGER		chosen, shown: INTEGER
	~~stayWins: INTEGER~~
	do		do
	~~games~~ := ~~1000000~~		create doors.make_filled (Door_count) -- False is a goat, True is a car
	~~create random.make~~		doors [next_random_door] := True -- Put a car behind a random door
			chosen := next_random_door -- Pick a door, any door

	~~across 1 \|..\| games as plays loop~~		-- Monty selects a door which is neither the winner nor the choice
	~~create doors.make_filled (3)~~ -- ~~False is~~ a ~~goat, True~~ is ~~a car~~		from
	~~random.forth~~		shown := next_random_door
	~~doors [random.item \\ 3 + 1]~~ := ~~True -- Put a car behind a random door~~		until
			shown /= chosen and not doors [shown]
	~~random.forth~~		loop
	~~chosen := random.item \\ 3 + 1 -- Pick a door, any door~~		shown := next_random_door
			end
	~~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		if doors [chosen] then -- If you would have won by staying, count it
	~~stay_wins~~ := ~~stay_wins~~ + 1		staying_wins := staying_wins + 1
	~~end~~
	end		end
			ensure
			staying_wins_valid: staying_wins = old staying_wins or staying_wins = old staying_wins + 1
			end

			feature {NONE} -- Implementation

	~~out ("Staying wins " + stay_wins + "~~ times.~~%N")~~		Door_count: INTEGER = 3
	~~out ("Switching wins " + games~~ - ~~stay_wins~~ + ~~" times.%N")~~		-- The total number of doors.

			staying_wins: INTEGER
			-- The number of times that the strategy of staying would win.

			random_generator: RANDOM
			-- A random number generator for selecting doors.

			next_random_door: INTEGER
			-- A door chosen at random.
			do
			random_generator.forth
			Result := random_generator.item \\ Door_count + 1
			ensure
			valid_door: Result >= 1 and Result <= Door_count
	end		end

Peter gummer at 00:15, 10 August 2012

2012-08-10T00:15:42Z

← Older revision		Revision as of 00:15, 10 August 2012
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	</e>		</e>

			==Comments==

	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?		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==~~

Peter gummer: /* Eiffel code */

2012-08-10T00:14:33Z

Eiffel code

← Older revision		Revision as of 00:14, 10 August 2012
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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==

Bmeyer at 17:25, 9 August 2012

2012-08-09T17:25:27Z

← Older revision		Revision as of 17:25, 9 August 2012
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	==Reference==		==Reference==
	Statement of the Monty Hall problem on RosettaCode: [http://rosettacode.org/wiki/Monty_Hall_problem here].		Statement of the Monty Hall problem on RosettaCode: [http://rosettacode.org/wiki/Monty_Hall_problem here].
	<p>Deadline for adding to RosettaCode page: 31 Aug 2012; submitter:		<br>Deadline for adding to RosettaCode page: 31 Aug 2012; submitter:

	==Eiffel code==		==Eiffel code==

	==Comments==		==Comments==

Bmeyer at 17:24, 9 August 2012

2012-08-09T17:24:14Z

← Older revision		Revision as of 17:24, 9 August 2012
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	==Eiffel code==		==Eiffel code==

	==Comments==		==Comments==

Manus at 17:24, 9 August 2012

2012-08-09T17:24:07Z

← Older revision		Revision as of 17:24, 9 August 2012
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	[[Category:Rosetta Code]]		[[Category:Rosetta Code]]
			[[Category:Flash Code ]]

	==Reference==		==Reference==

Bmeyer: /* Reference */

2012-08-09T17:22:45Z

Reference

← Older revision		Revision as of 17:22, 9 August 2012
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	==Reference==		==Reference==
	Statement of the Monty Hall problem on RosettaCode: [http://rosettacode.org/wiki/Monty_Hall_problem here].		Statement of the Monty Hall problem on RosettaCode: [http://rosettacode.org/wiki/Monty_Hall_problem here].
	Deadline for adding to RosettaCode page: 31 Aug 2012; submitter:		<p>Deadline for adding to RosettaCode page: 31 Aug 2012; submitter:

	==Eiffel code==		==Eiffel code==
	==Comments==		==Comments==