add graph implementation.

src/main/java/com/example/data_structure/service/GraphService.java

@@ -144,8 +144,48 @@ public class GraphService {
         visitStartNode.set(startVertex,startVertex);
         Stack<Integer> stack=new Stack<Integer>();
         stack.push(startVertex);
+        visited.set(startVertex,1);
+        visitSequence.add(startVertex);
+        steps.add(new GraphTraversalStep("visit",startVertex,startVertex,true));
+        boolean isTerminal=false;
+        int formerNode=0;
         while(!stack.isEmpty()){
-            boolean isTerminal=false;
+            int curVertex=stack.peek();
+            int nextNode=0;
+            if(visitSequence.get(visitSequence.size()-1)==curVertex) { //如果正在遍历某支路，没有折返
+                isTerminal=true;
+                for (int i = 0; i < nodeNum; i++) {
+                    if (content.get(curVertex).get(i) == 1) {
+                        if (visited.get(i) == 0) {
+                            nextNode = i;
+                            visited.set(nextNode, 1);
+                            visitSequence.add(nextNode);
+                            stack.push(nextNode);
+                            isTerminal = false;
+                            break;
+                        }
+                    }
+                }
+                if(isTerminal){
+                    formerNode=stack.pop();
+                }
+            }else{ //如果在折返状态中
+                if(formerNode<nodeNum-1) {
+                    boolean needReturn=true;
+                    for (int i = formerNode + 1; i < nodeNum; i++) {
+                        if(visited.get(i)==0){
+                            stack.push(i);
+                            visited.set(i,1);
+                            visitSequence.add(i);
+                            needReturn=false;
+                            break;
+                        }
+                    }
+                    if(needReturn){
+                        formerNode=stack.pop();
+                    }
+                }
+            }
         }
         return null;
     }