我希望有人可以帮助解决我遇到的问题。首先，我尝试删除尽可能多的代码，但这并没有导致问题。
我的问题是：当我运行程序时，一切都运行完美，直到我创建一个包含大约130个节点的图形。一旦它达到130多个节点，程序将永远在无限循环中运行。
我尝试在15处运行135个节点的程序，以获得所需的图形密度。
为了给出一些背景信息，我正致力于研究模拟，为此我创建了随机图并使用BFS构建生成树。
我的问题出现在生成树的过程中。
复制并粘贴代码并使用javac MMB.java编译所有文件。
import java.util.*;
/**
* Custom type Set used to differentiate nodes in the FAST and SLOW sets
*/
enum Set {
FAST, SLOW;
}
/**
* Custom node class used to store our spanning tree
*/
class Node<T> {
private T data;
private Node<T> parent;
private List<Node<T>> children;
private int level;
private int rank;
private Set set;
// constructor for root Nodes and stand alone nodes
public Node(T data){
this.data = data;
this.parent = null;
this.level = 0;
this.rank = Integer.MIN_VALUE;
this.children = new ArrayList<Node<T>>();
}
// constructor for all non root nodes
public Node(T data, Node<T> parent){
this.data = data;
this.setParent(parent);
this.level = (parent.getLevel()) + 1;
this.rank = Integer.MIN_VALUE;
this.children = new ArrayList<Node<T>>();
}
// get data
public T getData(){
return this.data;
}
// set data
public void setData(T data){
this.data = data;
}
// add child node
public void addChild(Node<T> child){
children.add(child);
}
// remove child node
public void removeChild(Node<T> child){
children.remove(child);
}
// get rank
public int getRank(){
return this.rank;
}
// set rank
public void setRank(int rank){
this.rank = rank;
}
// get parent
public Node<T> getParent(){
return this.parent;
}
// set parent - updates parent node to have child
public void setParent(Node<T> parent){
this.parent = parent;
parent.addChild(this);
}
// returns level of a Node
public int getLevel(){
return this.level;
}
// returns a list of children of a given node
public List<Node<T>> getChildren(){
return this.children;
}
// set the Set a node is in
public void setSet(Set set){
this.set = set;
}
// get the Set a node is in
public Set getSet(){
return this.set;
}
// returns the tree as a list of nodes using DFS traversal
public List<Node<T>> treeToList(){
List<Node<T>> list = new LinkedList<Node<T>>();
List<Node<T>> visitedNodes = new LinkedList<Node<T>>();
list.add(this);
while(list.size() > 0){
Node<T> currentNode = list.get(list.size() - 1);
List<Node<T>> currentNodesChildren = currentNode.getChildren();
if(!visitedNodes.contains(currentNode)){
for(Node<T> n : currentNodesChildren){
list.add(n);
}
visitedNodes.add(currentNode);
}
else {
list.remove(currentNode);
}
}
return visitedNodes;
}
// returns the number of levels in the tree
// Note: levels start at 0
public int numberOfLevels(){
List<Node<T>> list = this.treeToList();
int maxLevel = 0;
for(Node<T> n : list)
if(n.getLevel() > maxLevel)
maxLevel = n.getLevel();
return maxLevel + 1;
}
// returns the max rank in the tree
public int maxRank(){
List<Node<T>> list = this.treeToList();
int maxRank = 0;
for(Node<T> n : list)
if(n.getRank() > maxRank)
maxRank = n.getRank();
return maxRank;
}
// returns a list of nodes with a given rank and level in the FAST set
public List<Node<T>> nodeRankLevelSubset(int rank, int level){
List<Node<T>> list = this.treeToList();
List<Node<T>> subset = new LinkedList<Node<T>>();
for(Node<T> n : list)
if(n.getRank() == rank && n.getLevel() == level && n.getSet() == Set.FAST)
subset.add(n);
return subset;
}
// Print All
public void printAll(){
List<Node<T>> list = this.treeToList();
for(Node<T> n : list){
System.out.println("{");
System.out.println(" \"data\": " + n.getData() + ",");
System.out.println(" \"level\": " + n.getLevel() + ",");
System.out.println(" \"rank\": " + n.getRank() + ",");
switch(n.getSet()){
case FAST:
System.out.println(" \"set\": \"FAST\"");
break;
case SLOW:
System.out.println(" \"set\": \"SLOW\"");
break;
}
System.out.print(" \"parent\": ");
if(n.getParent() != null)
System.out.println(n.getParent().getData() + ",");
else
System.out.println(" ,");
System.out.print(" \"children\": [");
for(Node<T> cn : n.getChildren()){
System.out.print(cn.getData() + ",");
}
System.out.println("]\n}");
}
}
// BFS to print
public void printTree(){
List<Node<T>> discoveredNodes = new LinkedList<Node<T>>();
List<Node<T>> queue = new LinkedList<Node<T>>();
List<Node<T>> children;
Node<T> currentNode;
queue.add(this);
discoveredNodes.add(this);
while(queue.size() > 0){
currentNode = queue.remove(0);
children = currentNode.getChildren();
System.out.print("\n" + currentNode.getData() + ": ");
for(Node<T> n : children){
queue.add(n);
discoveredNodes.add(n);
System.out.print(n.getData() + " " + " Rank: " + n.getRank() + " ");
}
}
System.out.print("\n");
}
}
public class MMB {
// boolean 2D array used to make the edges in a random graph
public static boolean[][] randomGraph;
// custom Node class used to store our BFS spanning tree
public static Node<Integer> spanningTree;
public static void main(String[] args){
int numberOfNodes, graphDensity;
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the desired number of Nodes: ");
numberOfNodes = scanner.nextInt();
System.out.print("Enter the desired graph density: ");
graphDensity = scanner.nextInt();
randomGraph = randomGraph(numberOfNodes, graphDensity);
/* Print Out Graph */
for(int i = 0; i < randomGraph.length; i++){
System.out.print(i + " ");
for(int j = 0; j < randomGraph.length; j++){
System.out.printf(" " + randomGraph[i][j] + " ");
}
System.out.println("");
}
System.out.println("");
System.out.println("HERE - CREATED GRAPH");
spanningTree = spanningTree(0);
System.out.println("HERE - CREATED SPAnnING TREE");
// rankNodes(spanningTree, spanningTree.numberOfLevels());
// System.out.println("HERE - FIRST RANK");
// determineSet(spanningTree);
// System.out.println("HERE - DETERMINE SET");
// //spanningTree.printTree();
// reRankNodes(spanningTree);
// System.out.println("HERE - RERANK NODES");
// //spanningTree.printTree();
// spanningTree.printAll();
}
/**
* Create an undirected graph at random
* A 2D boolean array will represent the edges between nodes
* @param numberOfNodes number of nodes in the graph
* @param graphDensity integer percentage of graph density
*/
public static boolean[][] randomGraph(int numberOfNodes, int graphDensity){
boolean[][] graph = new boolean[numberOfNodes][numberOfNodes];
Random randomNumber = new Random();
boolean hasEdge;
for(int i = 0; i < numberOfNodes; i++){
hasEdge = false;
for(int j = 0; j < numberOfNodes; j++){
// i != j ensures no loops
if(i != j && (randomNumber.nextInt(100) + 1) < graphDensity){
graph[i][j] = true;
graph[j][i] = true;
hasEdge = true;
}
}
// to ensure no disconnected nodes, keep track with hasEdge
// if no edge exists create a random one
int randomNum;
while(!hasEdge){
if((randomNum = randomNumber.nextInt(numberOfNodes)) != i){
graph[i][randomNum] = true;
graph[randomNum][i] = true;
hasEdge = true;
}
}
}
return graph;
}
/**
* Create a Spanning Tree from an undirected graph using BFS
* A custom Node structure will represent our spanning tree
* @param root root of undirected graph from 0 to numberOfNodes-1
*/
public static Node<Integer> spanningTree(int root){
Node<Integer> tree = new Node<Integer>(root);
Node<Integer> currentNode;
Integer currentNodeData;
LinkedList<Node<Integer>> discoveredNodes = new LinkedList<Node<Integer>>();
LinkedList<Node<Integer>> queue = new LinkedList<Node<Integer>>();
queue.add(tree);
discoveredNodes.add(tree);
while(queue.size() > 0){
currentNode = queue.removeFirst();
currentNodeData = currentNode.getData();
for(int i = 0; i < randomGraph.length; i++){
if(randomGraph[currentNodeData][i] && !listContainsNode(discoveredNodes, i)){
Node<Integer> newNode = new Node<Integer>(i, currentNode);
queue.add(newNode);
discoveredNodes.add(newNode);
}
}
}
return tree;
}
/* Helper Methods */
// search a list of Nodes for a value
public static boolean listContainsNode(List<Node<Integer>> list, Integer data){
for(Node<Integer> n : list)
if(n.getData() == data)
return true;
return false;
}
}
答案 0 :(得分：1)
在cauda venenum
/* Helper Methods */
// search a list of Nodes for a value
public static boolean listContainsNode(List<Node<Integer>> list, Integer data){
for(Node<Integer> n : list)
if(n.getData() == data) // <-- Can you spot the bug?
return true;
return false;
}
问题是您将Integer与==进行了比较。如果数字低于128，则可以使用整数，但是对象上的比较不再有效。
只需使用：
if (n.getData().equals(data))
比较节点内容（并继续编写优秀的代码;） - 在StackOverflow的问题中看到这样的质量并不容易）
答案 1 :(得分：1)
好吧，我发现了一个潜在的危险代码，如果矩阵不会被平方，那么你应该使用
for(int i = 0; i < randomGraph[currentNodeData].length; i++){
而不是
for(int i = 0; i < randomGraph.length; i++){
我认为我可能会发现嵌套异常：）。
如果您使用的是Integer而不是int，则必须关注==运营商。 Java为值-127到128创建静态整数，但是当你到达它时，它不再起作用!!
此代码
Integer x;
Integer y;
x = 111;
y = 111;
System.out.println(x == y);
x = 130;
y = 130;
System.out.println(x == y);
有这个输出
true
false
使用equals是安全的，但是这段代码：
Integer x;
Integer y;
x = 111;
y = 111;
System.out.println(x.equals(y));
x = 130;
y = 130;
System.out.println(x.equals(y));
有这个输出
true
true