Add Tarjans Algorithm (#3874)

src/test/java/com/thealgorithms/datastructures/graphs/TarjansAlgorithmTest.java

@@ -0,0 +1,72 @@
+package com.thealgorithms.datastructures.graphs;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+public class TarjansAlgorithmTest {
+    
+    TarjansAlgorithm tarjansAlgo = new TarjansAlgorithm();
+
+    @Test
+    public void findStronglyConnectedComps(){
+        var v = 5;
+        var graph = new ArrayList<List<Integer>>();
+        for (int i = 0; i < v; i++) {
+            graph.add(new ArrayList<>());
+        }
+        graph.get(0).add(1);
+        graph.get(1).add(2);
+        graph.get(2).add(0);
+        graph.get(1).add(3);
+        graph.get(3).add(4);
+
+        var actualResult = tarjansAlgo.stronglyConnectedComponents(v, graph);
+        /*
+            Expected result: 
+            0, 1, 2
+            3
+            4 
+        */
+        List<List<Integer>> expectedResult = new ArrayList<>();
+
+        expectedResult.add(Arrays.asList(4));
+        expectedResult.add(Arrays.asList(3));
+        expectedResult.add(Arrays.asList(2, 1, 0));
+        assertTrue(expectedResult.equals(actualResult));
+    }
+
+    @Test
+    public void findStronglyConnectedCompsShouldGetSingleNodes() {
+        //Create a adjacency list of graph
+        var n = 8;
+        var adjList = new ArrayList<List<Integer>>(n);
+
+        for (int i = 0; i < n; i++) {
+            adjList.add(new ArrayList<>());
+        }
+
+        adjList.get(0).add(1);
+        adjList.get(1).add(2);
+        adjList.get(2).add(3);
+        adjList.get(3).add(4);
+        adjList.get(4).add(5);
+        adjList.get(5).add(6);
+        adjList.get(6).add(7);
+        adjList.get(7).add(0);
+
+        List<List<Integer>> actualResult = tarjansAlgo.stronglyConnectedComponents(n, adjList);
+        List<List<Integer>> expectedResult = new ArrayList<>();
+        /*
+            Expected result: 
+            7, 6, 5, 4, 3, 2, 1, 0
+        */
+        expectedResult.add(Arrays.asList(7, 6, 5, 4, 3, 2, 1, 0));
+        assertTrue(expectedResult.equals(actualResult));
+    }
+    
+}