some-advent-of-code: d115dc46423faa44e416b283d1e61b6d1ffc3d8b

     1: 
     2: import java.io.IOException;
     3: import java.nio.file.Files;
     4: import java.nio.file.InvalidPathException;
     5: import java.nio.file.Path;
     6: import java.nio.file.Paths;
     7: import java.util.HashSet;
     8: import java.util.LinkedList;
     9: import java.util.List;
    10: import java.util.Map;
    11: import java.util.Set;
    12: import java.util.TreeMap;
    13: 
    14: public class Exercise200101
    15: {
    16: 
    17: 	public static void main( String args[] )
    18: 	{
    19: 		final String here = "e20011.m ";
    20: 		if ( args.length < 1 )
    21: 		{
    22: 			throw new RuntimeException( here +"add a filename argument" );
    23: 		}
    24: 		String userSaysFile = args[ 0 ];
    25: 		List<String> fileLines = new LinkedList<>();
    26: 		try
    27: 		{
    28: 			Path where = Paths.get( userSaysFile );
    29: 			fileLines = Files.readAllLines( where );
    30: 		}
    31: 		catch ( IOException | InvalidPathException ie )
    32: 		{
    33: 			System.err.println( here +"couldn't read file "+ userSaysFile +" because "+ ie );
    34: 			return;
    35: 		}
    36: 		/*
    37: 		- interpretation of spec -
    38: 		for values in file
    39: 			partition into more and less than half of target
    40: 		for values in less than half
    41: 			for values in more than half
    42: 				if sum is target
    43: 					print less * more
    44: 		*/
    45: 		// gather
    46: 		Set<Integer> lessThanHalf = new HashSet<>();
    47: 		Set<Integer> moreThanHalf = new HashSet<>();
    48: 		Integer temp;
    49: 		int target = 2020, half = target /2;
    50: 		boolean seenExactlyHalfAlready = false;
    51: 		int lineNum = 0;
    52: 		for ( String line : fileLines )
    53: 		{
    54: 			lineNum += 1;
    55: 			try
    56: 			{
    57: 				temp = Integer.parseInt( line );
    58: 				if ( temp < half )
    59: 					lessThanHalf.add( temp );
    60: 				else if ( temp > half )
    61: 					moreThanHalf.add( temp );
    62: 				else if ( ! seenExactlyHalfAlready )
    63: 					seenExactlyHalfAlready = true; // no need to save it
    64: 				else
    65: 				{
    66: 					System.err.println( here +"exactly half twice, squared is "+ (temp * temp) );
    67: 					return;
    68: 				}
    69: 			}
    70: 			catch ( NumberFormatException nfe )
    71: 			{
    72: 				System.err.println( here +"handed a non int "+ line +" on "+ lineNum +" because "+ nfe );
    73: 				continue;
    74: 			}
    75: 		}
    76: 		// combinatoric
    77: 		for ( Integer lesser : lessThanHalf )
    78: 		{
    79: 			for ( Integer greater : moreThanHalf )
    80: 			{
    81: 				if ( (lesser + greater) == target )
    82: 				{
    83: 					System.err.println( here +"lesser is "+ lesser +" greater is "+ greater +" product is "+ (lesser * greater) );
    84: 					return;
    85: 				}
    86: 			}
    87: 		}
    88: 		System.out.println( here +"input had no pair that summed to "+ target );
    89: 	}
    90: }
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