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/*
* monty - Hacked-together tool to simulate the Monty Hall problem. Still can't
* get my head around it ;)
* Copyright (c) 2017 David Phillips <dbphillipsnz@gmail.com>
* All rights reserved
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
enum Strategy {
STRATEGY_STICK,
STRATEGY_CHANGE
};
unsigned int monty(int door_count, unsigned long plays, enum Strategy strategy)
{
unsigned int i = 0;
unsigned int wins = 0;
int prize = -1;
int choice = -1;
int remain = -1;
for (i = 0; i < plays; i++) {
prize = rand() % door_count;
choice = rand() % door_count;
/* Monty shall open all doors except two; the contestant's choice
* and pick one door to not open */
if (choice == prize) {
/* contestant was originally correct? Pick any other door aside
* from their choice to remain. Crude loop strategy, but pseudo-
* randomness should help ensure quick termination */
do {
remain = rand() % door_count;
} while (remain == choice);
} else {
/* contestant never originally picked prize door; the prize door
* remains */
remain = prize;
}
switch (strategy) {
case STRATEGY_STICK:
/* stick with current door */
break;
case STRATEGY_CHANGE:
/* `change` strategy: switch to remaining door */
choice = remain;
break;
default:
return -1;
}
if (choice == prize)
wins++;
}
return wins;
}
int main()
{
double ratio = 0;
int runs = 1000000;
int wins = 0;
int doors = 3;
srand(time(NULL));
/* "stick/stay/lazy" strategy */
wins = monty(doors, runs, STRATEGY_STICK);
ratio = ((double)wins) / runs;
printf("Stick : Won %d of %d (%.5f) success\n", wins, runs, ratio);
/* "change" strategy */
wins = monty(doors, runs, STRATEGY_CHANGE);
ratio = ((double)wins) / runs;
printf("Change: Won %d of %d (%.5f) success\n", wins, runs, ratio);
return 0;
}
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