persistence-number-find.hgn

#! /bin/sh
exec huginn -E "${0}" "${@}"
#! huginn

import Algorithms as algo;
import Text as text;
import Operators as oper;
import Progress as progress;

to_digit( char_ ) {
	return ( number( integer( char_ ) - integer( '0' ) ) );
}

persistence( num_ ) {
	n = 0;
	while ( true ) {
		s = string( num_ );
		if ( size( s ) == 1 ) {
			break;
		}
		n += 1;
		num_ = algo.reduce(
			algo.map(
				s,
				to_digit
			),
			oper.multiply,
			$1
		);
	}
	return ( n );
}

main( argv_ ) {
	limit = integer( argv_[1] );
	digits = ( ( $2, 3 ), ( $3, 2 ), ( $7, limit ), ( $8, limit ), ( $9, limit ) );
	parts = [];
	best = 1;

	for ( i, digit : algo.enumerate( digits ) ) {
		part = [];
		for ( repeat : algo.range( digit[1] ) ) {
			part.push( digit[0] ^ number( repeat ) );
		}
		parts.push( part );
	}

	for (
		trialDesc : progress.bar(
			algo.product(
				algo.range( 3 ),
				algo.range( 2 ),
				algo.range( limit ),
				algo.range( limit ),
				algo.range( limit )
			)
		)
	) {
		n = $1;
		for ( i, count : algo.enumerate( trialDesc ) ) {
			n *= parts[i][count];
		}
		current = persistence( n );
		if ( current > best ) {
			best = current;
			s = "";
			for ( digit, count : algo.zip( digits, trialDesc ) ) {
				s += text.repeat( string( digit[0] ), count );
			}
			print( "\n{} - {}\n".format( s, best + 1 ) );
		}
	}
	return ( 0 );
}