打印图形时的无限循环

Question

我正在尝试打印图中的所有顶点及其边。我已经使用了邻接列表表示图。我的代码是

#define MAX 1000
struct node
{
    int data;
    struct node *next;
};
struct node *arr[MAX];

void printGraph(int n)
{
    // n is the number of vertex
    int i;
    for(i=0;i<n;i++)
    {
        printf("The vertex %d is connected to");
        if(arr[i]->next==NULL)
            printf("no edges");
        else
        {
            struct node *tmp;
            for(tmp=arr[i];tmp!=NULL;tmp=tmp->next)
                printf("%d",tmp->data);
        }
        printf("n");
    }
}

每当我调用printGraph方法时，我的程序就会进入一个无限循环。错误可能在哪里？

---

I am adding my other methods. Please check them to see if I am properly creating a graph

---

void createEmptyGraph(int n)
{
// n is the number of vertices
int i;
for(i=0;i<n;i++)
{
    struct node *n;
    n=(struct node *)malloc(sizeof(struct node));
    n->data=i;
    n->next=NULL;
    arr[i]=n;
}
printf("nAn empty graph with %d vertices has been sreated",n);
printf("nNo edge is connected yet");
}
void addNode(int startVertex,int endVertex)
{
// For directed edges
struct node *n;
n=(struct node *)malloc(sizeof(struct node));
n->next=arr[startVertex];
arr[startVertex]->next=n;

printf("nAn edge between directed from %d to %d has been added",startVertex,endVertex);
}

Answer 1

可能是tmp!=NULL从未发生过？

Answer 2

n->next=arr[startVertex];
arr[startVertex]->next=n;

这段代码使tmp=NULL从不发生

可能是这样的：

n->next=arr[startVertex]->next;
arr[startVertex]->next=n;

Answer 3

如果arr[i]在循环内，这可能会永远循环for(tmp=arr[i];tmp!=NULL;tmp=tmp->next)：保持一个被访问的向量来检查和中断循环，类似于：

node *visited[MAX];
int nVis = 0;
bool cycle = false;
for(tmp=arr[i];tmp!=NULL && !cycle;tmp=tmp->next) {
  for (int j = 0; j < nVis; ++j)
   if (visited[j] == tmp) {
     cycle = true;
     break;
   }
 visited[nVis++] = tmp;
 ...
}