naive fisher yates shuffle

Author: jaebradley

src/main/java/problems/impl/FisherYatesShufflerImpl.java

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+package problems.impl;
+
+import problems.interfaces.FisherYatesShuffler;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Stack;
+
+/**
+ * Fisher-Yates Shuffle
+ *
+ * Write down the numbers from 1 through N.
+ * Pick a random number k between one and the number of unstruck numbers remaining (inclusive).
+ * Counting from the low end, strike out the kth number not yet struck out, and write it down at the end of a separate list.
+ * Repeat from step 2 until all the numbers have been struck out.
+ * The sequence of numbers written down in step 3 is now a random permutation of the original numbers.
+ *
+ * https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
+ */
+
+public class FisherYatesShufflerImpl implements FisherYatesShuffler {
+  @Override
+  public <T> List<T> shuffle(final List<T> values) {
+    final List<T> valuesToShuffle = new ArrayList<>(values);
+    final List<T> shuffledValues = new Stack<>();
+    while(valuesToShuffle.size() > 0) {
+      int randomIndex = (int) (Math.random() * (valuesToShuffle.size() - 1));
+      T value = valuesToShuffle.get(randomIndex);
+      shuffledValues.add(value);
+      valuesToShuffle.remove(randomIndex);
+    }
+    return shuffledValues;
+  }
+}

src/main/java/problems/interfaces/FisherYatesShuffler.java

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+package problems.interfaces;
+
+import java.util.List;
+
+public interface FisherYatesShuffler {
+  <T> List<T> shuffle(final List<T> values);
+}

src/test/java/problems/impl/FisherYatesShufflerImplTest.java

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+package problems.impl;
+
+import org.junit.Test;
+import problems.interfaces.FisherYatesShuffler;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+public class FisherYatesShufflerImplTest {
+
+  private final FisherYatesShuffler shuffler = new FisherYatesShufflerImpl();
+
+  @Test
+  public void testShuffle() {
+    final List<Integer> firstFiveNaturalNumbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
+    final List<Integer> shuffledFirstFiveNaturalNumbers = shuffler.shuffle(firstFiveNaturalNumbers);
+    assertEquals(firstFiveNaturalNumbers.size(), shuffledFirstFiveNaturalNumbers.size());
+    assertTrue(shuffledFirstFiveNaturalNumbers.containsAll(firstFiveNaturalNumbers));
+  }
+}