some-advent-of-code: 73a649674a6b499648d8d1427222c879de253b80

     1: 
     2: import java.io.IOException;
     3: import java.nio.file.*;
     4: import java.util.*;
     5: 
     6: public class Exercise210301
     7: {
     8: 
     9: 	public static void main(
    10: 			String args[]
    11: 	) {
    12: 		final String here = "e210301.m ";
    13: 		if ( args.length < 1 )
    14: 		{
    15: 			throw new RuntimeException( here +"add a filename argument" );
    16: 		}
    17: 		String userSaysFile = args[ 0 ];
    18: 		List<String> fileLines = new LinkedList<>();
    19: 		try
    20: 		{
    21: 			Path where = Paths.get( userSaysFile );
    22: 			fileLines = Files.readAllLines( where );
    23: 		}
    24: 		catch ( IOException | InvalidPathException ie )
    25: 		{
    26: 			System.err.println( here +"couldn't read file "+ userSaysFile +" because "+ ie );
    27: 			return;
    28: 		}
    29: 		/*
    30: 		- interpretation of spec -
    31: 		gamma is the more common bit, epsilon is the less common bit
    32: 		put these in a bit set and multiply the resulting binary number
    33: 		*/
    34: 		Exercise210301.interpretDiagnostic( fileLines );
    35: 	}
    36: 
    37: 
    38: 	private static void interpretDiagnostic(
    39: 			List<String> fileLines
    40: 	) {
    41: 		final int oneInd = 0, nilInd = oneInd +1;
    42: 		int[][] bitCounts = new int[ 2 ][ fileLines.get( 0 ).length() ];
    43: 		for ( int initInd = 0; initInd < bitCounts[ oneInd ].length; initInd++ )
    44: 		{
    45: 			bitCounts[ oneInd ][ initInd ] = 0;
    46: 			bitCounts[ nilInd ][ initInd ] = 0;
    47: 		}
    48: 
    49: 		// sum bits
    50: 		for ( String line : fileLines )
    51: 		{
    52: 			if ( line.isEmpty() )
    53: 				continue;
    54: 			for ( int charInd = 0; charInd < line.length(); charInd++ )
    55: 			{
    56: 				if ( line.charAt( charInd ) == '1' )
    57: 					bitCounts[ oneInd ][ charInd ] += 1;
    58: 				else // == 0
    59: 					bitCounts[ nilInd ][ charInd ] += 1;
    60: 			}
    61: 		}
    62: 
    63: 		// determine gamma and epsilon
    64: 		long gamma = 0L, epsilon = 0L, multiplier = 1;
    65: 		for ( int bitInd = bitCounts[ oneInd ].length -1; bitInd >= 0; bitInd-- )
    66: 		{
    67: 			if ( bitCounts[ oneInd ][ bitInd ] > bitCounts[ nilInd ][ bitInd ] )
    68: 				gamma += multiplier;
    69: 			else
    70: 				epsilon += multiplier;
    71: 			multiplier *= 2;
    72: 		}
    73: 
    74: 		System.out.println( "\tg"+ gamma +" e"+ epsilon +" t"+ gamma * epsilon );
    75: 	}
    76: 
    77: 
    78: }
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