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//================================================================================
// Monty.cpp
//--------------------------------------------------------------------------------
//
//================================================================================
#include <iostream>
#include <string>
#include <ctime>
using namespace std;
const int numDoors = 4; // using 1 - 3 array indexes, 0 will be ignored
void setup( bool doors[] );
int Open( int guess, bool doors[] ); // open a door other than guess which isn't the winning door
int SwapGuess( int guess, int openDoor, bool doors[] );
int GetRand( int min, int max );
bool PlayGame( bool swap );
//================================================================================
// main()
//--------------------------------------------------------------------------------
//
//================================================================================
int main()
{
int games = 100000;
double wins = 0;
// play games without swapping
for( int i = 0; i < games; i++ )
{
if( PlayGame( false ) )
wins++;
}
cout << "Not swapping win %" << 100 / (games/wins) << endl;
// play games with swapping
wins = 0;
for( int i = 0; i < games; i++ )
{
if( PlayGame( true ) )
wins++;
}
cout << "Swapping win %" << 100 / (games/wins) << endl;
}
//================================================================================
// PlayGame()
//--------------------------------------------------------------------------------
//
//================================================================================
bool PlayGame( bool swap )
{
bool doors[numDoors];
setup( doors );
int guess = -1;
guess = GetRand( 1, 3 );
int openDoor = -1;
openDoor = Open( guess, doors );
if( swap )
guess = SwapGuess( guess, openDoor, doors );
if( doors[guess] )
return true; // win
else
return false; // lose
}
//================================================================================
// setup()
//--------------------------------------------------------------------------------
//
//================================================================================
void setup( bool doors[] )
{
for( int i = 0; i < numDoors; i++ )
doors[i] = false;
doors[ GetRand( 1, numDoors-1) ] = true;
return;
}
//================================================================================
// Open()
//--------------------------------------------------------------------------------
// Open a door other than guess which isn't the winning door
//================================================================================
int Open( int guess, bool doors[] )
{
int d1 = -1;
int d2 = -1;
switch( guess )
{
case 1:
d1 = 2;
d2 = 3;
break;
case 2:
d1 = 1;
d2 = 3;
break;
case 3:
d1 = 1;
d2 = 2;
break;
}
if( doors[d1] || doors[d2] ) // one of the not chosen doors has the prize
{
if( doors[d1] ) // door d1 has the prize, open d2
return d2;
else
return d1;
}
// neither of the not chosen doors has the prize, open a random one
if( GetRand( 1, 2 ) == 1 )
return d1;
else
return d2;
}
//================================================================================
// SwapGuess()
//--------------------------------------------------------------------------------
//
//================================================================================
int SwapGuess( int guess, int openDoor, bool doors[] )
{
int newGuess = -1;
switch( guess )
{
case 1:
if( openDoor == 2 )
newGuess = 3;
else
newGuess = 2;
break;
case 2:
if( openDoor == 1 )
newGuess = 3;
else
newGuess = 1;
break;
case 3:
if( openDoor == 1 )
newGuess = 2;
else
newGuess = 1;
}
return newGuess;
}
//================================================================================
// GetRand()
//--------------------------------------------------------------------------------
// Return a random integer in the range of min to max
//================================================================================
int GetRand( int min, int max )
{
static bool initialized = false;
if( !initialized )
{
srand( time( 0 ) );
initialized = true;
}
return (rand() % (max - min + 1)) + min;
}
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