some-advent-of-code: cc6f3e18cd9a4a8748ae34af43249332dc58e409

     1: 
     2: import java.io.IOException;
     3: import java.nio.file.*;
     4: import java.util.*;
     5: 
     6: public class Exercise210302
     7: {
     8: 
     9: 	public static void main(
    10: 			String args[]
    11: 	) {
    12: 		final String here = "e210302.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: 		sum the bits individually, discard and resum as necessary
    32: 		*/
    33: 		Exercise210302.interpretDiagnostic( fileLines );
    34: 	}
    35: 
    36: 
    37: 	private static void interpretDiagnostic(
    38: 			List<String> fileLines
    39: 	) {
    40: 		int ones = 0, nils = 0;
    41: 		int oxygenRating = 0, carbonRating = 0;
    42: 		List<String> previousCandidates = new ArrayList<>( fileLines.size() );
    43: 		previousCandidates.addAll( fileLines );
    44: 		List<String> currentCandidates = new LinkedList<>();
    45: 		int len = fileLines.get( 0 ).length();
    46: 
    47: 		// oxygen
    48: 		for ( int charInd = 0; charInd < len; charInd++ )
    49: 		{
    50: 			ones = 0;
    51: 			nils = 0;
    52: 			for ( String line : previousCandidates )
    53: 			{
    54: 				if ( line.charAt( charInd ) == '1' )
    55: 					ones += 1;
    56: 				else // == 0
    57: 					nils += 1;
    58: 			}
    59: 
    60: 			char toMatch;
    61: 			if ( ones > nils )
    62: 				toMatch = '1';
    63: 			else if ( ones < nils )
    64: 				toMatch = '0';
    65: 			else
    66: 				toMatch = '='; // for clarity when comparing == below
    67: 			for ( String candidate : previousCandidates )
    68: 			{
    69: 				if ( candidate.charAt( charInd ) == toMatch
    70: 						|| ( ones == nils
    71: 							&& candidate.charAt( charInd ) == '1' ) )
    72: 					currentCandidates.add( candidate );
    73: 			}
    74: 			if ( currentCandidates.size() == 1 )
    75: 				break;
    76: 			previousCandidates.clear();
    77: 			previousCandidates.addAll( currentCandidates );
    78: 			currentCandidates.clear();
    79: 		}
    80: 		oxygenRating = Exercise210302.asInt( currentCandidates.get( 0 ) );
    81: 
    82: 		// carbon
    83: 		previousCandidates.clear();
    84: 		previousCandidates.addAll( fileLines );
    85: 		currentCandidates.clear();
    86: 		for ( int charInd = 0; charInd < len; charInd++ )
    87: 		{
    88: 			ones = 0;
    89: 			nils = 0;
    90: 			for ( String line : previousCandidates )
    91: 			{
    92: 				if ( line.charAt( charInd ) == '1' )
    93: 					ones += 1;
    94: 				else // == 0
    95: 					nils += 1;
    96: 			}
    97: 
    98: 			char toMatch;
    99: 			if ( ones < nils )
   100: 				toMatch = '1';
   101: 			else if ( ones > nils )
   102: 				toMatch = '0';
   103: 			else
   104: 				toMatch = '='; // for clarity when comparing == below
   105: 			for ( String candidate : previousCandidates )
   106: 			{
   107: 				if ( candidate.charAt( charInd ) == toMatch
   108: 						|| ( ones == nils
   109: 							&& candidate.charAt( charInd ) == '0' ) )
   110: 					currentCandidates.add( candidate );
   111: 			}
   112: 			if ( currentCandidates.size() == 1 )
   113: 				break;
   114: 			previousCandidates.clear();
   115: 			previousCandidates.addAll( currentCandidates );
   116: 			currentCandidates.clear();
   117: 		}
   118: 		carbonRating = Exercise210302.asInt( currentCandidates.get( 0 ) );
   119: 
   120: 		System.out.println( "\to"+ oxygenRating +" c"+ carbonRating +" t"+ oxygenRating * carbonRating );
   121: 	}
   122: 
   123: 
   124: 	private static int asInt(
   125: 			String bitChars
   126: 	) {
   127: 		int value = 0, multiplier = 1;
   128: 		for ( int charInd = bitChars.length() -1; charInd >= 0; charInd-- )
   129: 		{
   130: 			if ( bitChars.charAt( charInd ) == '1' )
   131: 				value += multiplier;
   132: 			multiplier *= 2;
   133: 		}
   134: 		return value;
   135: 	}
   136: 
   137: 
   138: }
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