aoc2020 day 23

23.js

const _ = require( 'lodash' );
let cups;
let current;
let max = 9;

function extract( current ) {
	let result = [
		cups[ current ]
	];
	result[ 1 ] = cups[ result[ 0 ] ];
	result[ 2 ] = cups[ result[ 1 ] ];
	cups[ current ] = cups[ result[ 2 ] ];

	return result;
}

function insert( destination, items ) {
	const _next = cups[ destination ];
	cups[ destination ] = items[ 0 ];
//	cups.set( items[ 0 ], items[ 1 ] );
//	cups.set( items[ 1 ], items[ 2 ] );
	cups[ items[ 2 ] ] = _next;
}

module.exports = {
	inputCast( line ) {
		cups = new Int32Array( line.length + 1 );
		const nr = line.split``.map( Number );
		for ( let i = 0; i < nr.length - 1; i ++ ) {
			cups[ nr[ i ] ] = nr[ i + 1 ];
		}
		cups[ _.last( nr ) ] = nr[ 0 ];
		current = nr[ 0 ];

		return line;
	},
	print( from = current ) {
		let value = from;
		let output = [];
		do {
			value = cups[ value ];
			output.push( value );
		} while ( value !== from );

		console.log( output.slice( 0, - 1 ).join`` );
	},
	game( moves = 100 ) {
		let move = 0;
		let destination;
		while ( move < moves ) {

			//1 . pick next 3 cups;
			const next = extract( current );

			//2. find destination
			destination = current - 1;
			while ( destination <= 0 || next.includes( destination ) ) {
				destination --;
				if ( destination <= 0 ) {
					destination = max;
				}
			}

			//3. insert cups
			insert( destination, next );
			current = cups[ current ];

			move ++;
		}
	},
	one( input ) {
		this.game( 100 );
		this.print( 1 );
	},
	two( input ) {
		cups = new Int32Array( 1000001 );
		max = 1000000;
		const nr = input[ 0 ].split``.map( Number );
		for ( let i = 0; i < nr.length - 1; i ++ ) {
			cups[ nr[ i ] ] = nr[ i + 1 ];
		}
		let last = _.last( nr );
		for ( let i = 10; i <= max; i ++ ) {
			cups[ last ] = i;
			last = i;
		}
		cups[ max ] = _.first( nr );
		this.game( max * 10 );

		return cups[ 1 ] * cups[ cups[ 1 ] ];
	}
};