Question

我想在bfs中找到树节点的高度，但它没有用完，它给了我前5个节点的正确高度，但最后两个节点不正确。这是代码

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package bfs;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

public class BreadthFirstSearchExample
{ 

 private Queue<Node> queue;
 static ArrayList<Node> nodes=new ArrayList<Node>();
 static class Node
 {
  int data;
  boolean visited;
  int parent;
  int height;

  Node(int data){
   this.data=data;


  }
 }

 public BreadthFirstSearchExample()
 {
  queue = new LinkedList<Node>();
 }

 // find neighbors of node using adjacency matrix
 // if adjacency_matrix[i][j]==1, then nodes at index i and index j are connected
 public ArrayList<Node> findNeighbours(int adjacency_matrix[][],Node x)
 {
  int nodeIndex=-1;

  ArrayList<Node> neighbours=new ArrayList<Node>();
  for (int i = 0; i < nodes.size(); i++) {
   if(nodes.get(i).equals(x))
   {
    nodeIndex=i;
    break;
   }
  }

  if(nodeIndex!=-1)
  {
   for (int j = 0; j < adjacency_matrix[nodeIndex].length; j++) {
    if(adjacency_matrix[nodeIndex][j]==1)
    {
     neighbours.add(nodes.get(j));
    }
   }
  }
  return neighbours;
 }

 public  void bfs(int adjacency_matrix[][], Node node)
 {

  queue.add(node);
  node.visited=true;


  int nf =0;

  while (!queue.isEmpty())
  {
   nf = queue.size();
   Node element=queue.remove();

   System.out.print(element.data + "\t");


    System.out.print("Height" + element.height + "\t");

   ArrayList<Node> neighbours=findNeighbours(adjacency_matrix,element);
   for (int i = 0; i < neighbours.size(); i++) {
    Node n=neighbours.get(i);
    int mf = neighbours.size();

    if(n!=null && !n.visited)
    {

     n.parent=element.data;
     queue.add(n);
     n.visited=true;   
    }
    n.height++;
   element.height = n.height;
   }

  }
 }

 public static void main(String arg[])
 {

   Node node40 =new Node(40);
   Node node10 =new Node(10);
   Node node20 =new Node(20);
   Node node30 =new Node(30);
   Node node60 =new Node(60);
   Node node50 =new Node(50);
   Node node70 =new Node(70);

   nodes.add(node40);
   nodes.add(node10);
   nodes.add(node20);
   nodes.add(node30);
   nodes.add(node60);
   nodes.add(node50);
   nodes.add(node70);
   int adjacency_matrix[][] = {
     {0,1,1,0,0,0,0},  // Node 1: 40
     {1,0,0,1,0,0,0},  // Node 2 :10
     {1,0,0,1,1,1,0},  // Node 3: 20
     {0,1,1,0,1,0,0},  // Node 4: 30
     {0,0,1,1,0,0,1},  // Node 5: 60
     {0,0,1,0,0,0,1},  // Node 6: 50
     {0,0,0,0,1,1,0},  // Node 7: 70
   };
   System.out.println("The BFS traversal of the graph is ");
   BreadthFirstSearchExample bfsExample = new BreadthFirstSearchExample();
   bfsExample.bfs(adjacency_matrix, node40);

 }
}

代码的输出应为

40 Height0 10 Height1 20 Height1 30 Height2 60 Height2 50 Height2 70 Height3

但是它给了我输出

40 Height0 10 Height1 20 Height1 30 Height2 60 Height2 50 Height1 70 Height2

我该如何解决这个问题？

Answer 1

bfs方法的for - 循环必须如下所示：

for (int i = 0; i < neighbours.size(); i++) {
  Node n = neighbours.get(i);
  int mf = neighbours.size();

  if (n != null && !n.visited) {
    n.parent = element.data;
    queue.add(n);
    n.visited = true;
    n.height = element.height + 1;    // <- this is right
  }

  // This was wrong
  //n.height++;                    
  //element.height = n.height;
}

<强>解释

更改的行将被访问节点的高度（“n”）设置为父节点（“element”）的高度+ 1，但仅在第一次访问时（因此在if语句内）。这就是你想要的，即高度。

您之前所做的是每次将节点视为邻居时增加节点的高度，无论之前是否被访问过。然后将父节点的高度更改为该高度，但从未看到它，因为它不会再次打印。

Answer 2

只需从

更改此部分即可

if(n!=null && !n.visited)
{
    n.parent=element.data;
    queue.add(n);
    n.visited=true;
}
n.height++;
element.height = n.height;

到

if(n!=null && !n.visited)
{
    n.parent=element.data;
    queue.add(n);
    n.visited=true;
    n.height=element.height+1;
}
//n.height++;
//element.height = n.height;

在bfs树中查找节点的高度

2 个答案: