elegant stream solution

src/main/java/Solution.java

@@ -1,20 +1,59 @@
 import java.util.*;
-import java.io.*;
-import java.math.*;
+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 );
-		// read values with in.next...() methods
-		
-		// code your solution here
+		var digits = new Scanner( System.in ).tokens()
+				.map( Integer::valueOf )
+				.collect( Collectors.toList() );
 		
-		// Write result with System.out.println()
-		System.out.println( "value" );
+		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();
+	}
+	
+	/** 
+	 * 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 int byLine( int index ) {
+		return index / SIZE;
+	}
+	
+	private static int byRow( int index ) {
+		return index % SIZE;
+	}
+	
+	private static int byBlock( int index ) {
+		return byRow( index ) / BLOCK_SIZE + ( index / ( SIZE * BLOCK_SIZE )) * BLOCK_SIZE;
+	}
+	
 }