Optimization

src/main/java/io/github/deepeshpatel/jnumbertools/generator/permutation/UniquePermutationInSizeRange.java

@@ -0,0 +1,65 @@
+/*
+ * JNumberTools Library
+ * Copyright (c) 2021 Deepesh Patel (patel.deepesh@gmail.com)
+ */
+package io.github.deepeshpatel.jnumbertools.generator.permutation;
+
+
+import io.github.deepeshpatel.jnumbertools.generator.AbstractGenerator;
+import io.github.deepeshpatel.jnumbertools.generator.subset.SubsetGenerator;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+
+public class UniquePermutationInSizeRange<T> extends AbstractGenerator<T> {
+
+
+    private final int fromInclusive;
+    private final int toInclusive;
+
+    public UniquePermutationInSizeRange(Collection<T> seed, int fromInclusive, int toInclusive) {
+        super(seed);
+        this.fromInclusive = fromInclusive;
+        this.toInclusive = toInclusive;
+    }
+
+    @Override
+    public Iterator<List<T>> iterator() {
+       return new OnDemandIterator();
+    }
+
+    private class OnDemandIterator implements Iterator<List<T>> {
+
+        final Iterator<List<T>> subsetIterator;
+        Iterator<List<T>> currentIterator;
+        public OnDemandIterator() {
+            subsetIterator = new SubsetGenerator<>(seed, fromInclusive, toInclusive).iterator();
+            getNextIterator();
+        }
+
+        @Override
+        public boolean hasNext() {
+            if(currentIterator.hasNext()) {
+                return true;
+            }
+
+            if(!subsetIterator.hasNext()) {
+                return false;
+            }
+
+            return getNextIterator().hasNext();
+
+        }
+
+        private Iterator<List<T>> getNextIterator(){
+            currentIterator = new UniquePermutation<>(subsetIterator.next()).iterator();
+            return currentIterator;
+        }
+
+        @Override
+        public List<T> next() {
+            return currentIterator.next();
+        }
+    }
+}

src/test/java/io/github/deepeshpatel/jnumbertools/generator/permutation/UniquePermutationInSizeRangeTest.java

@@ -0,0 +1,36 @@
+package io.github.deepeshpatel.jnumbertools.generator.permutation;
+
+import io.github.deepeshpatel.jnumbertools.generator.JNumberTools;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+public class UniquePermutationInSizeRangeTest {
+
+    @Test
+    public void shouldGenerateAllPermutationsInSizeRange2To3() {
+
+        int from = 0;
+        int to = 3;
+        List<Integer> input = IntStream.range(0,4).boxed().collect(Collectors.toList());
+
+        List<List<Integer>> outputViaKPermutation = new ArrayList<>();
+        for(int i=from; i<=to; i++) {
+            List<List<Integer>> collect = JNumberTools.permutationsOf(input)
+                    .k(i)
+                    .stream().collect(Collectors.toList());
+            outputViaKPermutation.addAll(collect);
+        }
+
+        List<List<Integer>> output = JNumberTools.permutationsOf(input)
+                .uniqueInSizeRange(from, to)
+                .stream().collect(Collectors.toList());
+
+        Assert.assertEquals(outputViaKPermutation.toString(), output.toString());
+
+    }
+}