通过邻接表进行前序遍历

Question

我正在尝试将我的 EdgeList 转换为 Adjacency List，然后 preorder traverse 通过它。我很确定到 Adjacency List 的转换工作正常，但我在 preorder traversing 上遇到了麻烦。我试图用 DFS 来做，但它给了我错误的结果。

这是我的优势：

{index1=0, index2=2}
{index1=3, index2=4}
{index1=1, index2=4}
{index1=0, index2=5}
{index1=2, index2=6}
{index1=1, index2=5}
{index1=2, index2=7}

这就是链表的样子。

或

linked[2, 5]
linked[4, 5]
linked[6, 7]
linked[4]

现在我想预序遍历图，得到结果0 - 2 - 6 - 7 - 5 - 1 - 4 - 3。

          0
      2       5
   6    7       1
                  4
                   3

我已经尝试在我的 AdjacencyListGraph 中使用 DFS，但这是我使用此代码 0 2 6 7 5 得到的结果：

public class AdjacencyListGraph {

    private int V;   // No. of vertices

    // Array  of lists for Adjacency List Representation
    private LinkedList<Integer> adj[];

    // Constructor
    AdjacencyListGraph(int v) {
        V = v;
        adj = new LinkedList[v];
        for (int i=0; i<v; ++i)
            adj[i] = new LinkedList();
    }

    //Function to add an edge into the graph
    void addEdge(int v, int w) {
        adj[v].add(w);  // Add w to v's list.
    }


    // A function used by DFS
    void DFSUtil(int v,boolean visited[])
    {
        // Mark the current node as visited and print it
        visited[v] = true;
        System.out.print(v+" ");

        // Recur for all the vertices adjacent to this vertex
        Iterator<Integer> i = adj[v].listIterator();
//        System.out.println(i.toString());
        while (i.hasNext())
        {
            int n = i.next();
            if (!visited[n])
                DFSUtil(n,visited);
        }
    }

    // The function to do DFS traversal. It uses recursive DFSUtil()
    void DFS(int v)
    {

        // Mark all the vertices as not visited(set as
        // false by default in java)
        boolean visited[] = new boolean[V];

        // Call the recursive helper function to print DFS traversal
        // starting from all vertices one by one

        DFSUtil(v, visited);
    }

    public static void main(String[] args) {
        AdjacencyListGraph graph = new AdjacencyListGraph(8);

        graph.addEdge(0, 2);
        graph.addEdge(0, 5);
        graph.addEdge(1, 4);
        graph.addEdge(1, 5);
        graph.addEdge(2, 6);
        graph.addEdge(2, 7);
        graph.addEdge(3, 4);

        graph.DFS(0);
    }
}

我也试过使用：

void DFS() 
{ 
    // Mark all the vertices as not visited(set as 
    // false by default in java) 
    boolean visited[] = new boolean[V]; 

    // Call the recursive helper function to print DFS traversal 
    // starting from all vertices one by one 
    for (int i=0; i<V; ++i) 
        if (visited[i] == false) 
            DFSUtil(i, visited); 
}

而不是上面提到的那个，它遍历了所有 nodes，但它 returns 结果顺序错误。

我哪里做错了，我应该如何或使用什么来获得预期的结果？

Answer 1

试试这张图：

graph.addEdge(0, 2);
graph.addEdge(0, 5);
graph.addEdge(1, 4);
graph.addEdge(5, 1); // different direction than original
graph.addEdge(2, 6);
graph.addEdge(2, 7);
graph.addEdge(4, 3); // different direction than original

或者，对程序中的 addEdge 方法稍作修改：

//Function to add an edge into the graph
void addEdge(int v, int w) {
    adj[v].add(w);  // Add w to v's list.
    adj[w].add(v);  // Add v to w's list.
}

通过邻接表进行前序遍历

Preorder traversal through Adjacency List

java

graph

adjacency-list

depth-first-search

preorder