Update Graph.java

for dfsWithoutRecursion, when a node popped from the stack it should be checked that the current node is visited or not. Since stack has duplicated nodes, some nodes is visired doubly.

algorithms-searching/src/main/java/com/baeldung/algorithms/dfs/Graph.java

@@ -29,6 +29,7 @@ public class Graph {
         stack.push(start);
         while (!stack.isEmpty()) {
             int current = stack.pop();
+            if(!isVisited[current]){
                 isVisited[current] = true;
                 visit(current);
                 for (int dest : adjVertices.get(current)) {
@@ -37,6 +38,7 @@ public class Graph {
                 }
             }
         }
+    }
 
     public void dfs(int start) {
         boolean[] isVisited = new boolean[adjVertices.size()];