Galton box animation: Difference between revisions

=={{header|Java}}==

The balls keep track of where they are, and we just have to move them down and print. You might easily adjust this to take command line input for the numbers of pins and balls. I'm sure that this could be a lot shorter...

<lang Java>import java.util.Random;

import java.util.List;

import java.util.ArrayList;

public class GaltonBox {

public static void main( final String[] args ) {

new GaltonBox( 8, 200 ).run();

}

private final int m_pinRows;

private final int m_startRow;

private final Position[] m_balls;

private final Random m_random = new Random();

public GaltonBox( final int pinRows, final int ballCount ) {

m_pinRows = pinRows;

m_startRow = pinRows + 1;

m_balls = new Position[ ballCount ];

for ( int ball = 0; ball < ballCount; ball++ )

m_balls[ ball ] = new Position( m_startRow, 0, 'o' );

}

private static class Position {

int m_row;

int m_col;

char m_char;

Position( final int row, final int col, final char ch ) {

m_row = row;

m_col = col;

m_char = ch;

}

}

public void run() {

for ( int ballsInPlay = m_balls.length; ballsInPlay > 0; ) {

ballsInPlay = dropBalls();

print();

}

}

private int dropBalls() {

int ballsInPlay = 0;

int ballToStart = -1;

// Pick a ball to start dropping

for ( int ball = 0; ball < m_balls.length; ball++ )

if ( m_balls[ ball ].m_row == m_startRow )

ballToStart = ball;

// Drop balls that are already in play

for ( int ball = 0; ball < m_balls.length; ball++ )

if ( ball == ballToStart ) {

m_balls[ ball ].m_row = m_pinRows;

ballsInPlay++;

}

else if ( m_balls[ ball ].m_row > 0 && m_balls[ ball ].m_row != m_startRow ) {

m_balls[ ball ].m_row -= 1;

m_balls[ ball ].m_col += m_random.nextInt( 2 );

if ( 0 != m_balls[ ball ].m_row )

ballsInPlay++;

}

return ballsInPlay;

}

private void print() {

for ( int row = m_startRow; row --> 1; ) {

for ( int ball = 0; ball < m_balls.length; ball++ )

if ( m_balls[ ball ].m_row == row )

printBall( m_balls[ ball ] );

System.out.println();

printPins( row );

}

printCollectors();

System.out.println();

}

private static void printBall( final Position pos ) {

for ( int col = pos.m_row + 1; col --> 0; )

System.out.print( ' ' );

for ( int col = 0; col < pos.m_col; col++ )

System.out.print( " " );

System.out.print( pos.m_char );

}

private void printPins( final int row ) {

for ( int col = row + 1; col --> 0; )

System.out.print( ' ' );

for ( int col = m_startRow - row; col --> 0; )

System.out.print( ". " );

System.out.println();

}

private void printCollectors() {

final List<List<Position>> collectors = new ArrayList<List<Position>>();

for ( int col = 0; col < m_startRow; col++ ) {

final List<Position> collector = new ArrayList<Position>();

collectors.add( collector );

for ( int ball = 0; ball < m_balls.length; ball++ )

if ( m_balls[ ball ].m_row == 0 && m_balls[ ball ].m_col == col )

collector.add( m_balls[ ball ] );

}

for ( int row = 0, rows = longest( collectors ); row < rows; row++ ) {

for ( int col = 0; col < m_startRow; col++ ) {

final List<Position> collector = collectors.get( col );

final int pos = row + collector.size() - rows;

System.out.print( '|' );

if ( pos >= 0 )

System.out.print( collector.get( pos ).m_char );

else

System.out.print( ' ' );

}

System.out.println( '|' );

}

}

private static final int longest( final List<List<Position>> collectors ) {

int result = 0;

for ( final List<Position> collector : collectors )

result = Math.max( collector.size(), result );

return result;

}

}</lang>

{{out}}

When only five balls have begun to fall through the pins:

<pre> o

.

o

. .

o

. . .

o

. . . .

o

. . . . .

. . . . . .

. . . . . . .

. . . . . . . . </pre>

Later, some balls have arrived in the collectors:

<pre> o

.

o

. .

o

. . .

o

. . . .

o

. . . . .

o

. . . . . .

o

. . . . . . .

o

. . . . . . . .

| | | | | |o| | | |

| | | |o|o|o| | | |</pre>

Note that the collectors are as deep as required.

Finally, all the balls are in the collectors:

<pre> .

. .

. . .

. . . .

. . . . .

. . . . . .

. . . . . . .

. . . . . . . .

| | | | |o| | | | |

| | | | |o| | | | |

| | | | |o| | | | |

| | | | |o| | | | |

| | | | |o| | | | |

| | | | |o| | | | |

| | | | |o| | | | |

| | | | |o| | | | |

| | | |o|o| | | | |

| | | |o|o| | | | |

| | | |o|o| | | | |

| | | |o|o| | | | |

| | | |o|o| | | | |

| | | |o|o| | | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o| | | |

| | | |o|o|o|o| | |

| | | |o|o|o|o| | |

| | | |o|o|o|o| | |

| | | |o|o|o|o| | |

| | | |o|o|o|o| | |

| | | |o|o|o|o| | |

| | | |o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o| | |

| | |o|o|o|o|o|o| |

| | |o|o|o|o|o|o| |

| | |o|o|o|o|o|o| |

| |o|o|o|o|o|o|o| |

| |o|o|o|o|o|o|o| |

| |o|o|o|o|o|o|o| |</pre>