BAEL-5646: String permutation examples (#12595)

algorithms-modules/algorithms-miscellaneous-4/src/main/java/com/baeldung/algorithms/stringpermutation/ArrayHelper.java

@@ -0,0 +1,14 @@
+package com.baeldung.algorithms.stringpermutation;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class ArrayHelper {
+
+    private ArrayHelper() {
+    }
+
+    static List<Character> toCharacterList(final String string) {
+        return string.chars().mapToObj(s -> ((char) s)).collect(Collectors.toList());
+    }
+}

algorithms-modules/algorithms-miscellaneous-4/src/main/java/com/baeldung/algorithms/stringpermutation/StringPermutationsApache.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.stringpermutation;
+
+import java.util.Collection;
+import java.util.List;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.collections4.iterators.PermutationIterator;
+
+public class StringPermutationsApache {
+
+    public Collection<List<Character>> eagerPermutationWithRepetitions(final String string) {
+        final List<Character> characters = ArrayHelper.toCharacterList(string);
+        return CollectionUtils.permutations(characters);
+    }
+
+    public PermutationIterator<Character> lazyPermutationWithoutRepetitions(final String string) {
+        final List<Character> characters = ArrayHelper.toCharacterList(string);
+        return new PermutationIterator<>(characters);
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-4/src/main/java/com/baeldung/algorithms/stringpermutation/StringPermutationsCombinatoricsLib.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.stringpermutation;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import org.paukov.combinatorics3.Generator;
+import org.paukov.combinatorics3.PermutationGenerator.TreatDuplicatesAs;
+
+public class StringPermutationsCombinatoricsLib {
+
+    public List<List<Character>> permutationWithoutRepetitions(final String string) {
+        List<Character> chars = ArrayHelper.toCharacterList(string);
+        return Generator.permutation(chars)
+            .simple()
+            .stream()
+            .collect(Collectors.toList());
+    }
+
+    public List<List<Character>> permutationWithRepetitions(final String string) {
+        List<Character> chars = ArrayHelper.toCharacterList(string);
+        return Generator.permutation(chars)
+            .simple(TreatDuplicatesAs.IDENTICAL)
+            .stream()
+            .collect(Collectors.toList());
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-4/src/main/java/com/baeldung/algorithms/stringpermutation/StringPermutationsGuava.java

@@ -0,0 +1,18 @@
+package com.baeldung.algorithms.stringpermutation;
+
+import com.google.common.collect.Collections2;
+import java.util.Collection;
+import java.util.List;
+
+public class StringPermutationsGuava {
+
+    public Collection<List<Character>> permutationWithRepetitions(final String string) {
+        final List<Character> characters = ArrayHelper.toCharacterList(string);
+        return Collections2.permutations(characters);
+    }
+public Collection<List<Character>> permutationWithoutRepetitions(final String string) {
+    final List<Character> characters = ArrayHelper.toCharacterList(string);
+    return Collections2.orderedPermutations(characters);
+}
+
+}