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  1. import java.util.ArrayList;
  2. import java.util.Arrays;
  3. import java.util.List;
  4. import java.util.stream.Collectors;
  5.  
  6. class Combination {
  7.     private List<List<List<String>>> pairs = new ArrayList<>();
  8.  
  9.     public Combination( List<String> elements ) {
  10.         this.pairs = createPairsFromElements( elements );
  11.     }
  12.  
  13.     private Combination() {
  14.     }
  15.  
  16.     public static Combination createFromPairs( String[][] arrPairs ) {
  17.         Combination combination = new Combination();
  18.         combination.pairs = createPairsFromArrayPairs(arrPairs);
  19.         return combination;
  20.     }
  21.  
  22.     /**
  23.      * Create the pairs based on the String[][]
  24.      *
  25.      * Add the empty option at the beginner of each group
  26.      * Create the Lists and group them again
  27.      *
  28.      * @param arrPairs
  29.      * @return pairs
  30.      */
  31.     private static List<List<List<String>>> createPairsFromArrayPairs( String[][] arrPairs ) {
  32.         List<List<List<String>>> pairs = new ArrayList<>();
  33.  
  34.         for ( String[] groupValue: arrPairs ) {
  35.  
  36.             List<List<String>> listGroupValue = new ArrayList<>();
  37.  
  38.             /* add the empty value to the pairs */
  39.             listGroupValue.add(Arrays.asList());
  40.  
  41.             for ( String value: groupValue ) {
  42.  
  43.                 List<String> listValue = Arrays.asList( value );
  44.                 listGroupValue.add( listValue );
  45.  
  46.             }
  47.  
  48.             pairs.add( listGroupValue );
  49.         }
  50.         return pairs;
  51.  
  52.     }
  53.  
  54.     /**
  55.      * Convert the string list "a", "b", "c" to
  56.      * this:
  57.      * [
  58.      *  [ [], [a] ], [ [], [b] ], [ [], [c] ]
  59.      * ]
  60.      *
  61.      * @param elements List of values to the collection
  62.      * @return pairs
  63.      */
  64.     private static List<List<List<String>>> createPairsFromElements( List<String> elements ) {
  65.         return elements.stream().map(
  66.                 (String value) -> {
  67.                     List<List<String>> values = Arrays.asList(
  68.                             Arrays.asList(),            // immutable empty list
  69.                             Arrays.asList( value )      // immutable atomic list
  70.                     );
  71.                     return values;
  72.                 }
  73.         ).collect(Collectors.toList());
  74.     }
  75.  
  76.     /**
  77.      * Get the combination without restriction
  78.      *
  79.      * @param size
  80.      * @return
  81.      */
  82.     public List<List<String>> getCombination( int size ) {
  83.         return this.getCombination( size, false );
  84.     }
  85.  
  86.     /**
  87.      /*
  88.      * Combine every pair of elements creating a big list
  89.      * [ [], [b] ] x [ [], [a] ] = [ ([] + []), ([] + [a]), ([b] + []), ([b] + [a])) ] =
  90.      * [ [], [a], [b], [a, b] ]
  91.      * This keep working until add all elements.
  92.      *
  93.      * We filter to remove the combinations that are bigger than the max size
  94.      *
  95.      * @param size Max size of each result list
  96.      * @param restricted Should be exactly the received size.
  97.      * @return List of combinations
  98.      */
  99.     public List<List<String>> getCombination( int size, boolean restricted ) {
  100.  
  101.         List<List<String>> result = pairs.parallelStream().reduce(
  102.             new ArrayList<>(),
  103.             (acc,current) -> {
  104.                 if( acc.size() == 0 ) {
  105.                     return current;
  106.                 }
  107.  
  108.                 List<List<String>> combinations = new ArrayList<>();
  109.  
  110.                 current.stream().forEach(
  111.                     (List<String> valueCurrent ) -> acc.stream().forEach(
  112.                         (List<String> valueAcc) -> {
  113.                             List<String> combination = new ArrayList<>();
  114.                             combination.addAll( valueAcc );
  115.                             combination.addAll( valueCurrent );
  116.                             if( combination.size() <= size ) {
  117.                                 combinations.add( combination );
  118.                             }
  119.                         }
  120.                     )
  121.                 );
  122.                 return combinations;
  123.             }
  124.         );
  125.  
  126.         if( ! restricted ) {
  127.             return result;
  128.         }
  129.  
  130.         /* if the combination is size restricted, filter only elements with the exactly size */
  131.         return result.stream().filter( combination -> combination.size() == size ).
  132.                 collect(Collectors.toList());
  133.     }
  134. }
  135.  
  136. public class Main {
  137.  
  138.     public static void main( String[] param ) {
  139.  
  140.         Combination combination = new Combination(Arrays.asList("A","B","C","D","E"));
  141.  
  142.         /* show all the combinations from 0 to 3 elements */
  143.         System.out.println( combination.getCombination(3));
  144.         // [
  145.         //  [],
  146.         //  [A],
  147.         //  [B], [A, B],
  148.         //  [C], [A, C], [B, C], [A, B, C],
  149.         //  [D], [A, D], [B, D], [A, B, D], [C, D], [A, C, D], [B, C, D],
  150.         //  [E], [A, E], [B, E], [A, B, E], [C, E], [A, C, E], [B, C, E], [D, E], [A, D, E], [B, D, E], [C, D, E]
  151.         // ]
  152.  
  153.  
  154.         /* show all the combinations with exactly 4 elements */
  155.         System.out.println( combination.getCombination(4, true));
  156.         // [
  157.         //   [A, B, C, D],
  158.         //   [A, B, C, E],
  159.         //   [A, B, D, E],
  160.         //   [A, C, D, E],
  161.         //   [B, C, D, E]
  162.         // ]
  163.  
  164.  
  165.         Combination other = Combination.createFromPairs(
  166.                 new String[][]{{"1","2","3"},{"4","5","6"},{"7","8","9"},{"10","11","12"} }
  167.         );
  168.  
  169.  
  170.         /* show all the combinations with exactly 3 elements */
  171.         System.out.println( other.getCombination(3, true));
  172.         // [
  173.         //  [1, 4, 7], [2, 4, 7], [3, 4, 7], [1, 5, 7] ...
  174.         //  ...  [3, 9, 12], [4, 9, 12], [5, 9, 12], [6, 9, 12]
  175.         // ]
  176.  
  177.     }
  178. }
  179.  
Success #stdin #stdout 0.21s 34984KB
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[[], [A], [B], [A, B], [C], [A, C], [B, C], [A, B, C], [D], [A, D], [B, D], [A, B, D], [C, D], [A, C, D], [B, C, D], [E], [A, E], [B, E], [A, B, E], [C, E], [A, C, E], [B, C, E], [D, E], [A, D, E], [B, D, E], [C, D, E]]
[[A, B, C, D], [A, B, C, E], [A, B, D, E], [A, C, D, E], [B, C, D, E]]
[[1, 4, 7], [2, 4, 7], [3, 4, 7], [1, 5, 7], [2, 5, 7], [3, 5, 7], [1, 6, 7], [2, 6, 7], [3, 6, 7], [1, 4, 8], [2, 4, 8], [3, 4, 8], [1, 5, 8], [2, 5, 8], [3, 5, 8], [1, 6, 8], [2, 6, 8], [3, 6, 8], [1, 4, 9], [2, 4, 9], [3, 4, 9], [1, 5, 9], [2, 5, 9], [3, 5, 9], [1, 6, 9], [2, 6, 9], [3, 6, 9], [1, 4, 10], [2, 4, 10], [3, 4, 10], [1, 5, 10], [2, 5, 10], [3, 5, 10], [1, 6, 10], [2, 6, 10], [3, 6, 10], [1, 7, 10], [2, 7, 10], [3, 7, 10], [4, 7, 10], [5, 7, 10], [6, 7, 10], [1, 8, 10], [2, 8, 10], [3, 8, 10], [4, 8, 10], [5, 8, 10], [6, 8, 10], [1, 9, 10], [2, 9, 10], [3, 9, 10], [4, 9, 10], [5, 9, 10], [6, 9, 10], [1, 4, 11], [2, 4, 11], [3, 4, 11], [1, 5, 11], [2, 5, 11], [3, 5, 11], [1, 6, 11], [2, 6, 11], [3, 6, 11], [1, 7, 11], [2, 7, 11], [3, 7, 11], [4, 7, 11], [5, 7, 11], [6, 7, 11], [1, 8, 11], [2, 8, 11], [3, 8, 11], [4, 8, 11], [5, 8, 11], [6, 8, 11], [1, 9, 11], [2, 9, 11], [3, 9, 11], [4, 9, 11], [5, 9, 11], [6, 9, 11], [1, 4, 12], [2, 4, 12], [3, 4, 12], [1, 5, 12], [2, 5, 12], [3, 5, 12], [1, 6, 12], [2, 6, 12], [3, 6, 12], [1, 7, 12], [2, 7, 12], [3, 7, 12], [4, 7, 12], [5, 7, 12], [6, 7, 12], [1, 8, 12], [2, 8, 12], [3, 8, 12], [4, 8, 12], [5, 8, 12], [6, 8, 12], [1, 9, 12], [2, 9, 12], [3, 9, 12], [4, 9, 12], [5, 9, 12], [6, 9, 12]]
https://ideone.com/sSRrY3
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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