Created
April 30, 2019 10:57
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Generate non-repetetive permutations of given numbers and utilize each combination. Example result for 4: 4! = 24 combinations
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import java.util.*; | |
class Permutations { | |
public static void main(final String[] args) { | |
// Permutations of the numbers 0 to 3 to get all possible combinations. | |
// For 4 numbers the result should be 4! = 24 different combinations | |
// like 1-2-3-4, 1-2-4-3, 1-3-2-4, 1-3-4-2, etc. | |
Collection<List<Integer>> permutations = new Permutations() | |
.generatePermutationsWithoutRepetition(new HashSet<>(Arrays.asList(0, 1, 2, 3))); | |
permutations.forEach(perm -> { | |
System.out.println(perm.get(0)); | |
System.out.println(perm.get(1)); | |
System.out.println(perm.get(2)); | |
System.out.println(perm.get(3)); | |
}); | |
} | |
public <T> Collection<List<T>> generatePermutationsWithoutRepetition(Set<T> availableNumbers) { | |
Collection<List<T>> permutations = new HashSet<>(); | |
for (T number : availableNumbers) { | |
Set<T> numbers = new HashSet<>(availableNumbers); | |
numbers.remove(number); | |
if (!numbers.isEmpty()) { | |
Collection<List<T>> childPermutations = generatePermutationsWithoutRepetition(numbers); | |
for (List<T> childPermutation : childPermutations) { | |
List<T> permutation = new ArrayList<>(); | |
permutation.add(number); | |
permutation.addAll(childPermutation); | |
permutations.add(permutation); | |
} | |
} else { | |
List<T> permutation = new ArrayList<>(); | |
permutation.add(number); | |
permutations.add(permutation); | |
} | |
} | |
return permutations; | |
} | |
} |
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