From adf21ab0c87bffd1c774072335a7d9d4f62fcee4 Mon Sep 17 00:00:00 2001
From: Hardik Pawar <97388607+Hardvan@users.noreply.github.com>
Date: Tue, 15 Oct 2024 14:18:48 +0530
Subject: [PATCH] feat: Add `CelebrityFinder` new algorithm with Junit tests
(#5756)
---
DIRECTORY.md | 2 +
.../thealgorithms/stacks/CelebrityFinder.java | 52 +++++++++++++++++++
.../stacks/CelebrityFinderTest.java | 41 +++++++++++++++
3 files changed, 95 insertions(+)
create mode 100644 src/main/java/com/thealgorithms/stacks/CelebrityFinder.java
create mode 100644 src/test/java/com/thealgorithms/stacks/CelebrityFinderTest.java
diff --git a/DIRECTORY.md b/DIRECTORY.md
index cb26c292b..11ce5b744 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -607,6 +607,7 @@
* [WiggleSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/WiggleSort.java)
* stacks
* [BalancedBrackets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/BalancedBrackets.java)
+ * [CelebrityFinder](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/CelebrityFinder.java)
* [DecimalToAnyUsingStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/DecimalToAnyUsingStack.java)
* [DuplicateBrackets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/DuplicateBrackets.java)
* [InfixToPostfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/InfixToPostfix.java)
@@ -1163,6 +1164,7 @@
* [WiggleSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/WiggleSortTest.java)
* stacks
* [BalancedBracketsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/BalancedBracketsTest.java)
+ * [CelebrityFinderTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/CelebrityFinderTest.java)
* [DecimalToAnyUsingStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/DecimalToAnyUsingStackTest.java)
* [DuplicateBracketsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/DuplicateBracketsTest.java)
* [InfixToPostfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/InfixToPostfixTest.java)
diff --git a/src/main/java/com/thealgorithms/stacks/CelebrityFinder.java b/src/main/java/com/thealgorithms/stacks/CelebrityFinder.java
new file mode 100644
index 000000000..67ac861ef
--- /dev/null
+++ b/src/main/java/com/thealgorithms/stacks/CelebrityFinder.java
@@ -0,0 +1,52 @@
+package com.thealgorithms.stacks;
+
+import java.util.Stack;
+
+/**
+ * Solves the celebrity problem using a stack-based algorithm.
+ *
+ * Celebrity is someone known by everyone but doesn't know anyone else.
+ *
Applications: Graph theory and social network analysis.
+ *
+ * @author Hardvan
+ */
+public final class CelebrityFinder {
+ private CelebrityFinder() {
+ }
+
+ /**
+ * Finds the celebrity in the given party matrix using a stack-based algorithm.
+ *
+ * @param party A 2D matrix where party[i][j] is 1 if i knows j, otherwise 0.
+ * @return The index of the celebrity, or -1 if there is no celebrity.
+ */
+ public static int findCelebrity(int[][] party) {
+
+ // Push all people onto the stack
+ Stack stack = new Stack<>();
+ for (int i = 0; i < party.length; i++) {
+ stack.push(i);
+ }
+
+ // Find the potential celebrity by comparing pairs
+ while (stack.size() > 1) {
+ int person1 = stack.pop();
+ int person2 = stack.pop();
+
+ if (party[person1][person2] == 1) {
+ stack.push(person2); // person1 knows person2, so person2 might be the celebrity
+ } else {
+ stack.push(person1); // person1 doesn't know person2, so person1 might be the celebrity
+ }
+ }
+
+ // Verify the candidate
+ int candidate = stack.pop();
+ for (int i = 0; i < party.length; i++) {
+ if (i != candidate && (party[candidate][i] == 1 || party[i][candidate] == 0)) {
+ return -1;
+ }
+ }
+ return candidate;
+ }
+}
diff --git a/src/test/java/com/thealgorithms/stacks/CelebrityFinderTest.java b/src/test/java/com/thealgorithms/stacks/CelebrityFinderTest.java
new file mode 100644
index 000000000..da0217940
--- /dev/null
+++ b/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 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));
+ }
+}