translation: Add Python and Java code for EN version (#1345)

* Add the intial translation of code of all the languages

* test

* revert

* Remove

* Add Python and Java code for EN version

en/codes/java/chapter_graph/graph_dfs.java

@@ -0,0 +1,51 @@
+/**
+ * File: graph_dfs.java
+ * Created Time: 2023-02-12
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_graph;
+
+import java.util.*;
+import utils.*;
+
+public class graph_dfs {
+    /* Depth-first traversal helper function */
+    static void dfs(GraphAdjList graph, Set<Vertex> visited, List<Vertex> res, Vertex vet) {
+        res.add(vet);     // Record visited vertex
+        visited.add(vet); // Mark the vertex as visited
+        // Traverse all adjacent vertices of that vertex
+        for (Vertex adjVet : graph.adjList.get(vet)) {
+            if (visited.contains(adjVet))
+                continue; // Skip already visited vertices
+            // Recursively visit adjacent vertices
+            dfs(graph, visited, res, adjVet);
+        }
+    }
+
+    /* Depth-first traversal */
+    // Use adjacency list to represent the graph, to obtain all adjacent vertices of a specified vertex
+    static List<Vertex> graphDFS(GraphAdjList graph, Vertex startVet) {
+        // Vertex traversal sequence
+        List<Vertex> res = new ArrayList<>();
+        // Hash set, used to record visited vertices
+        Set<Vertex> visited = new HashSet<>();
+        dfs(graph, visited, res, startVet);
+        return res;
+    }
+
+    public static void main(String[] args) {
+        /* Initialize undirected graph */
+        Vertex[] v = Vertex.valsToVets(new int[] { 0, 1, 2, 3, 4, 5, 6 });
+        Vertex[][] edges = { { v[0], v[1] }, { v[0], v[3] }, { v[1], v[2] },
+                             { v[2], v[5] }, { v[4], v[5] }, { v[5], v[6] } };
+        GraphAdjList graph = new GraphAdjList(edges);
+        System.out.println("\nAfter initialization, the graph is");
+        graph.print();
+
+        /* Depth-first traversal */
+        List<Vertex> res = graphDFS(graph, v[0]);
+        System.out.println("\nDepth-first traversal (DFS) vertex sequence is");
+        System.out.println(Vertex.vetsToVals(res));
+    }
+}