Merge pull request #9 from jaebradley/minimum-absolute-difference

Minimum absolute difference

codereview/minimumAbsoluteDifferenceIdentifier.md

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+## Problem
+
+From [this Hackerrank problem](https://www.hackerrank.com/challenges/minimum-absolute-difference-in-an-array).
+
+> Given an array of N integers, find and print the minimum absolute difference between any two elements in the array.
+
+## Approach
+
+1. If there are less than two values in the array, throw an `IllegalArgumentException`. It's hard to find a difference
+   between `0` or `1` integers.
+2. Sort the input array.
+3. Set the initial minimum absolute difference to the absolute value of the difference between the value in index `1`
+   and the value in index `0`.
+4. Iterate through the sorted array and see if the absolute difference between two indices are less than the current
+   absolute difference. If so, this absolute difference becomes the new minimum value.
+5. Return the minimum value.
+
+## Implementation
+
+<!-- language: lang-java -->
+    public class MinimumAbsoluteDifferenceIdentifier {
+        public static int identifyMinimumAbsoluteDifference(int[] values) {
+            if (values.length <= 1) {
+                throw new IllegalArgumentException("Array must have at least two elements");
+            }
+
+            Arrays.sort(values);
+
+            int minimumAbsoluteDifference = Math.abs(values[1] - values[0]);
+
+            for (int i = 1, j = 2; j < values.length; i = j - 1, j++, i++) {
+                int absoluteDifference = Math.abs(values[j] - values[i]);
+
+                if (absoluteDifference < minimumAbsoluteDifference) {
+                    minimumAbsoluteDifference = absoluteDifference;
+                }
+            }
+
+            return minimumAbsoluteDifference;
+        }
+    }

src/main/java/algorithms/implementations/MinimumAbsoluteDifferenceIdentifier.java

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+package algorithms.implementations;
+
+import java.util.Arrays;
+
+/**
+ * https://www.hackerrank.com/challenges/minimum-absolute-difference-in-an-array
+ *
+ * Given an array of N integers, find and print the minimum absolute difference between any two elements in the array.
+ */
+
+public class MinimumAbsoluteDifferenceIdentifier {
+    public static int identifyMinimumAbsoluteDifference(int[] values) {
+        if (values.length <= 1) {
+            throw new IllegalArgumentException("Array must have at least two elements");
+        }
+
+        Arrays.sort(values);
+
+        int minimumAbsoluteDifference = Math.abs(values[1] - values[0]);
+
+        for (int i = 1, j = 2; j < values.length; i = j - 1, j++, i++) {
+            int absoluteDifference = Math.abs(values[j] - values[i]);
+
+            if (absoluteDifference < minimumAbsoluteDifference) {
+                minimumAbsoluteDifference = absoluteDifference;
+            }
+        }
+
+        return minimumAbsoluteDifference;
+    }
+}

src/test/java/algorithms/implementations/MinimumAbsoluteDifferenceIdentifierTest.java

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+package algorithms.implementations;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class MinimumAbsoluteDifferenceIdentifierTest {
+    @Test
+    public void testMinimumAbsoluteDifference() {
+        final int[] values = new int[] { 3, -7, 0 };
+        assertEquals(3, MinimumAbsoluteDifferenceIdentifier.identifyMinimumAbsoluteDifference(values));
+    }
+
+    @Test
+    public void itThrowsForEmptyValues() {
+        try {
+            MinimumAbsoluteDifferenceIdentifier.identifyMinimumAbsoluteDifference(new int[] {});
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+    }
+
+    @Test
+    public void itReturnsMinimumAbsoluteDifferenceForTwoElementArray() {
+        final int[] values = new int[] { 3, -7 };
+        assertEquals(10, MinimumAbsoluteDifferenceIdentifier.identifyMinimumAbsoluteDifference(values));
+    }
+}