BAEL-8771 Count the Number of Sign Changes in an Array

Author: yabetancourt

core-java-modules/core-java-arrays-operations-basic-3/src/test/java/com/baeldung/signchanges/SignChangesInAnArrayUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.signchanges;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.stream.IntStream;
+
+public class SignChangesInAnArrayUnitTest {
+
+    int[] sampleArray = {1, -2, -3, 4, 0, -1, 5};
+
+    int countSignChanges(int[] arr) {
+        if (arr == null || arr.length < 2) {
+            return 0;
+        }
+        int count = 0;
+
+        int prevSign = Integer.signum(arr[0]);
+
+        for (int i = 1; i < arr.length; i++) {
+            int currentSign = Integer.signum(arr[i]);
+
+            if (currentSign != 0 && prevSign != 0 && currentSign != prevSign) {
+                count++;
+            }
+
+            if (currentSign != 0) {
+                prevSign = currentSign;
+            }
+        }
+
+        return count;
+    }
+
+    @Test
+    void givenArray_whenExistsSignChanges_thenReturnSignChangesQuantity() {
+        int result = countSignChanges(sampleArray);
+        Assertions.assertThat(result).isEqualTo(4);
+    }
+
+    int countSignChangesStream(int[] arr) {
+        if (arr == null || arr.length < 2) {
+            return 0;
+        }
+
+        int[] signs = Arrays.stream(arr)
+            .map(Integer::signum)
+            .filter(s -> s != 0)
+            .toArray();
+
+        return (int) IntStream.range(1, signs.length)
+            .filter(i -> signs[i] != signs[i - 1])
+            .count();
+    }
+
+    @Test
+    void givenArray_whenUsingStreams_thenReturnSignChangesQuantity() {
+        int result = countSignChangesStream(sampleArray);
+        Assertions.assertThat(result).isEqualTo(4);
+    }
+
+}