feat: Add CelebrityFinder new algorithm with Junit tests (#5756)

src/test/java/com/thealgorithms/stacks/CelebrityFinderTest.java

@@ -0,0 +1,41 @@
+package com.thealgorithms.stacks;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class CelebrityFinderTest {
+
+    @ParameterizedTest
+    @MethodSource("providePartyMatrices")
+    public void testCelebrityFinder(int[][] party, int expected) {
+        assertEquals(expected, CelebrityFinder.findCelebrity(party));
+    }
+
+    private static Stream<Arguments> providePartyMatrices() {
+        return Stream.of(
+            // Test case 1: Celebrity exists
+            Arguments.of(new int[][] {{0, 1, 1}, {0, 0, 1}, {0, 0, 0}}, 2),
+
+            // Test case 2: No celebrity
+            Arguments.of(new int[][] {{0, 1, 0}, {1, 0, 1}, {1, 1, 0}}, -1),
+
+            // Test case 3: Everyone knows each other, no celebrity
+            Arguments.of(new int[][] {{0, 1, 1}, {1, 0, 1}, {1, 1, 0}}, -1),
+
+            // Test case 4: Single person, they are trivially a celebrity
+            Arguments.of(new int[][] {{0}}, 0),
+
+            // Test case 5: All know the last person, and they know no one
+            Arguments.of(new int[][] {{0, 1, 1, 1}, {0, 0, 1, 1}, {0, 0, 0, 1}, {0, 0, 0, 0}}, 3),
+
+            // Test case 6: Larger party with no celebrity
+            Arguments.of(new int[][] {{0, 1, 1, 0}, {1, 0, 0, 1}, {0, 1, 0, 1}, {1, 1, 1, 0}}, -1),
+
+            // Test case 7: Celebrity at the start of the matrix
+            Arguments.of(new int[][] {{0, 0, 0}, {1, 0, 1}, {1, 1, 0}}, 0));
+    }
+}