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Author SHA1 Message Date
Lothar Buchholz 8bd7d827a8 elegant stream solution 4 years ago

@ -1,71 +1,59 @@
import java.util.*;
import java.util.function.IntFunction;
import java.util.stream.*;
/**
* Template code to help you parse the standard input
* according to the problem statement.
**/
class Solution {
private static final int SIZE = 9;
private static final int BLOCK_SIZE = 3;
public static void main( String[] args ) {
Scanner in = new Scanner( System.in );
int[][] grid = new int[9][9];
for ( int index = 0; in.hasNext(); index++ ) {
int row = index / 9;
int col = index % 9;
grid[row][col] = in.nextShort();
}
var digits = new Scanner( System.in ).tokens()
.map( Integer::valueOf )
.collect( Collectors.toList() );
System.out.println( checkHorizontally( grid )
&& checkVertically( grid )
&& checkAllBlocks( grid )
);
System.out.println( checkSudoku( digits ));
}
/**
* The basic idea is to split the digits into groups that can be verified by the same logic over and over again.
* The code will create 27 groups - 9 lines, 9 rows and 9 blocks - and checks for all digits in each group.
*/
private static boolean checkSudoku( List<Integer> digits ) {
return Stream.of(
filterGroup( digits, Solution::byLine ),
filterGroup( digits, Solution::byRow ),
filterGroup( digits, Solution::byBlock )
).flatMap( Collection::stream )
.allMatch( Solution::checkAllDigits );
}
/**
* Splitting is done with a grouping function that calculates the group number for a grid index.
*/
private static Collection<List<Integer>> filterGroup( List<Integer> digits, IntFunction<Integer> grpFunc ) {
var group = IntStream.range( 0, digits.size() ).boxed()
.collect( Collectors.groupingBy( grpFunc::apply, Collectors.mapping( digits::get, Collectors.toList() )));
return group.values();
}
private static boolean checkHorizontally( int[][] grid ) {
//noinspection ForLoopReplaceableByForEach
for ( int r = 0; r < grid.length; r++ ) {
BitSet bs = new BitSet( 9 );
for ( int c = 0; c < grid[r].length; c++ ) {
bs.set( grid[r][c] );
}
if ( bs.cardinality() != 9 ) return false;
}
return true;
/**
* Checks if every digit from 1 to 9 is present in each group.
*/
private static boolean checkAllDigits( List<Integer> group ) {
return group.stream().distinct().count() == SIZE;
}
private static boolean checkVertically( int[][] grid ) {
for ( int c = 0; c < 9; c++ ) {
BitSet bs = new BitSet( 9 );
//noinspection ForLoopReplaceableByForEach
for ( int r = 0; r < grid.length; r++ ) {
bs.set( grid[r][c] );
}
if ( bs.cardinality() != 9 ) return false;
}
return true;
private static int byLine( int index ) {
return index / SIZE;
}
private static boolean checkAllBlocks( int[][] grid ) {
return checkBlock( grid, 0, 0 )
&& checkBlock( grid, 0, 3 )
&& checkBlock( grid, 0, 6 )
&& checkBlock( grid, 3, 0 )
&& checkBlock( grid, 3, 3 )
&& checkBlock( grid, 3, 6 )
&& checkBlock( grid, 6, 0 )
&& checkBlock( grid, 6, 3 )
&& checkBlock( grid, 6, 6 );
private static int byRow( int index ) {
return index % SIZE;
}
private static boolean checkBlock( int[][] block, int indexTop, int indexLeft ) {
BitSet bs = new BitSet( 9 );
for ( int r = indexTop; r < indexTop + 3; r++ ) {
for ( int c = indexLeft; c < indexLeft + 3; c++ ) {
bs.set( block[r][c] );
}
}
return ( bs.cardinality() == 9 );
private static int byBlock( int index ) {
return byRow( index ) / BLOCK_SIZE + ( index / ( SIZE * BLOCK_SIZE )) * BLOCK_SIZE;
}
}

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