add jUnit test and refactoring for CelebrityProblem.java

src/main/java/com/rampatra/arrays/CelebrityProblem.java

@@ -26,7 +26,9 @@ public class CelebrityProblem {
      * @param b
      * @return
      */
-    public static boolean haveAcquaintance(int[][] peoples, int a, int b) {
+
+    // Rename Method: haveAcquaintance -> doesKnow, for better clarity
+    public static boolean doesKnow(int[][] peoples, int a, int b) {
         return peoples[a][b] == 1;
     }
 
@@ -48,36 +50,45 @@ public static boolean haveAcquaintance(int[][] peoples, int a, int b) {
      * @param peoples
      * @return
      */
-    public static int findCelebrity(int[][] peoples) {
 
+    // Extract Method: Extract the possible celebrity finding logic into a new method
+    private static Stack<Integer> findPossibleCelebrities(int[][] peoples) {
         Stack<Integer> possibleCelebrities = new LinkedStack<>();
 
         for (int i = 0; i < peoples.length; i++) {
             for (int j = 0; j < peoples[0].length; j++) {
-                if (haveAcquaintance(peoples, i, j)) {
+                if (doesKnow(peoples, i, j)) {
                     possibleCelebrities.push(j);
                 }
             }
         }
-
+        return possibleCelebrities;
+    }
+    // Extract Method: Extract the celebrity finding logic into a new method
+    private static int findCelebrityInStack(Stack<Integer> possibleCelebrities, int[][] peoples) {
         int firstPerson = -1, secondPerson;
+
         while (!possibleCelebrities.isEmpty()) {
             firstPerson = possibleCelebrities.pop();
-
             // we have found the celebrity
-            if (possibleCelebrities.isEmpty()) break;
-
+            if (possibleCelebrities.isEmpty()) {
+                break;
+            }
             secondPerson = possibleCelebrities.pop();
-            if (haveAcquaintance(peoples, firstPerson, secondPerson)) {
+            if (doesKnow(peoples, firstPerson, secondPerson)) {
                 possibleCelebrities.push(secondPerson);
             } else {
                 possibleCelebrities.push(firstPerson);
             }
         }
-
         return firstPerson;
     }
 
+    public static int findCelebrity(int[][] peoples) {
+        Stack<Integer> possibleCelebrities = findPossibleCelebrities(peoples);
+        return findCelebrityInStack(possibleCelebrities, peoples);
+    }
+
     public static void main(String[] args) {
         System.out.println(findCelebrity(new int[][]{{0, 0, 1, 0}, {0, 0, 1, 0}, {0, 0, 0, 0}, {0, 0, 1, 0}}));
         System.out.println(findCelebrity(new int[][]{{0, 0, 0, 1}, {0, 0, 0, 1}, {0, 0, 0, 1}, {0, 0, 0, 1}}));

src/test/java/CelebrityProblemTest.java

@@ -0,0 +1,41 @@
+import com.rampatra.arrays.CelebrityProblem;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class CelebrityProblemTest {
+    @Test
+    public void testThereNoPerson() {
+        int[][] peoples = new int[][]{};
+        Assertions.assertEquals(-1, CelebrityProblem.findCelebrity(peoples));
+    }
+    @Test
+    public void testThereOnlyOnePerson() {
+        int[][] peoples = new int[][]{{0}};
+        Assertions.assertEquals(-1, CelebrityProblem.findCelebrity(peoples));
+    }
+    @Test
+    public void testNoCelebrity() {
+        int[][] peoples = new int[][]{{0, 1, 1, 0},{0, 0, 1, 0},{0, 0, 0, 1},{0, 0, 1, 0}};
+        Assertions.assertEquals(-1, CelebrityProblem.findCelebrity(peoples));
+    }
+    @Test
+    public void testCelebrityAtPosition0() {
+        int[][] peoples = new int[][]{{0, 0, 0, 0},{1, 0, 1, 0},{1, 0, 0, 1},{1, 0, 1, 0}};
+        Assertions.assertEquals(0, CelebrityProblem.findCelebrity(peoples));
+    }
+    @Test
+    public void testCelebrityAtPosition1() {
+        int[][] peoples = new int[][]{{0, 1, 1, 0},{0, 0, 0, 0},{0, 1, 0, 0},{0, 1, 1, 0}};
+        Assertions.assertEquals(1, CelebrityProblem.findCelebrity(peoples));
+    }
+    @Test
+    public void testCelebrityAtPosition2() {
+        int[][] peoples = new int[][]{{0, 1, 1, 0},{0, 0, 1, 0},{0, 0, 0, 0},{0, 1, 1, 0}};
+        Assertions.assertEquals(2, CelebrityProblem.findCelebrity(peoples));
+    }
+    @Test
+    public void testCelebrityAtPosition3() {
+        int[][] peoples = new int[][]{{0, 0, 1, 1},{0, 0, 1, 1},{1, 0, 0, 1},{0, 0, 0, 0}};
+        Assertions.assertEquals(3, CelebrityProblem.findCelebrity(peoples));
+    }
+}