我正在编写关于java中prim的算法扩展的程序。我正在使用以下书籍算法，第4版中的代码。 我的问题如下： 在运行时，for循环读取所有边缘直到最后一个循环才循环，它只读取第一行 运行程序后，我得到以下结果和错误：
0 0.71000 1 0.46000 2 0.80000 3 0.36000 4 0.26000 5 0.57000 6 0.68000 7 0.85000 16 0 4 五 0.35 4-5 0.35000
线程“main”中的异常java.lang.ArrayIndexOutOfBoundsException：4
at EdgeWeightedGraph.addEdge(EdgeWeightedGraph.java:207)
at EdgeWeightedGraph.<init>(EdgeWeightedGraph.java:152)
at PrimMST.main(PrimMST.java:174)
这是文件。感谢
import java.util.*;
import java.io.*;
public class EdgeWeightedGraph {
private final int V;
//private double VertexCost;
private int E;
//private int degree;
private Bag<Edge>[] adj;
private ArrayList<Vertex> vertex;
//private ArrayList<Edge>[] adj;
/**
* Initializes an empty edge-weighted graph with <tt>V</tt> vertices and 0 edges.
*/
public EdgeWeightedGraph( int V ) {
//vertex = new ArrayList<Vertex>();
if (V < 0) throw new IllegalArgumentException("Number of vertices must be nonnegative");
//if (VertexCost < 0) throw new IllegalArgumentException("The cost of the vertices must be nonnegative");
this.V = V;
// (Bag<Edge>[])
this.E = 0;
adj = (Bag<Edge>[]) new Bag[V];
//vertex = new ArrayList<Vertex>();
for (int v = 0; v < V; v++) {
adj[v] = new Bag<Edge>();
// System.out.println(adj[v]);
}
}
/**
* Initializes a random edge-weighted graph with <tt>V</tt> vertices and <em>E</em> edges.
* param V the number of vertices
* param E the number of edges
*/
public EdgeWeightedGraph(int V, int E) {
this(V);
if (E < 0) throw new IllegalArgumentException("Number of edges must be nonnegative");
// for (int j = 0; j < V; j++) {
// double cost = Math.round(100 * Math.random()) / 100.0;
//Vertex u = new Vertex(v,cost);
//vertex.add(u);
//}
for (int i = 0; i < E; i++) {
int v = (int) (Math.random() * V);
int w = (int) (Math.random() * V);
double weight = Math.round(100 * Math.random()) / 100.0;
Edge e = new Edge(v, w, weight);
addEdge(e);
}
}
/**
* Initializes an edge-weighted graph from an input stream.
*/
public EdgeWeightedGraph(In in) {
// this(in.readInt());
vertex = new ArrayList<Vertex>();
adj = (Bag<Edge>[]) new Bag[vertex.size()];
V = in.readInt();
E = in.readInt();
//System.out.println(adj);
//System.out.println(E);
for (int j =0;j < V; j++){
int v = in.readInt();
// System.out.println(v);
double cost = in.readDouble();
Vertex u = new Vertex(v, cost);
// System.out.println( cost);
vertex.add(u); //addVertex(v)
System.out.println(u);
}
if (E < 0) throw new IllegalArgumentException("Number of edges must be nonnegative");
System.out.println(E);
for (int i = 0; i < E; i++) {
System.out.println(i);
int v = in.readInt();
System.out.println(v);
int w = in.readInt();
System.out.println(w);
double weight = in.readDouble();
System.out.println(weight);
Edge e = new Edge(v, w, weight);
//System.out.println(e);
addEdge(e);
}
}
/**
* Initializes a new edge-weighted graph that is a deep copy of <tt>G</tt>.
*/
public EdgeWeightedGraph(EdgeWeightedGraph G) {
this(G.V());
this.E = G.E();
for (int v = 0; v < G.V(); v++) {
// reverse so that adjacency list is in same order as original
Stack<Edge> reverse = new Stack<Edge>();
for (Edge e : G.adj[v]) {
reverse.push(e);
}
for (Edge e : reverse) {
adj[v].add(e);
}
}
}
/**
* Returns the number of vertices in the edge-weighted graph.
*/
public int V() {
return V;
}
/**
* Returns the number of edges in the edge-weighted graph.
public int E() {
return E;
}
/**
* Adds the undirected edge <tt>e</tt> to the edge-weighted graph.
*
*/
public void addEdge(Edge e) {
int v = e.either();
int w = e.other(v);
if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
if (w < 0 || w >= V) throw new IndexOutOfBoundsException("vertex " + w + " is not between 0 and " + (V-1));
adj[v].add(e);
adj[w].add(e);
E++;
}
/**
* Returns the edges incident on vertex <tt>v</tt>.
*/
public Iterable<Edge> adj(int v) {
if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
return adj[v];
}
//return the vertex degree at each vertex in the graph
public int VertexDegree(){
int VertexDegree=0;
for ( int v =0; v<V; v++){
for ( Edge e : adj[v]){
//for(int i=0; i <= adj[v];i++) {
// degree+=1;
VertexDegree = adj[v].size();
}
}
return VertexDegree();
}
/**
* Returns all edges in the edge-weighted graph.
*/
public Iterable<Edge> edges() {
Bag<Edge> list = new Bag<Edge>();
for (int v = 0; v < V; v++) {
int selfLoops = 0;
for (Edge e : adj(v)) {
if (e.other(v) > v) {
list.add(e);
}
// only add one copy of each self loop (self loops will be consecutive)
else if (e.other(v) == v) {
if (selfLoops % 2 == 0) list.add(e);
selfLoops++;
}
}
}
return list;
}
/**
* Returns a string representation of the edge-weighted graph.
*/
public String toString() {
String NEWLINE = System.getProperty("line.separator");
StringBuilder s = new StringBuilder();
s.append(V + " " + E + NEWLINE);
for (int v = 0; v < V; v++) {
s.append(v + ": ");
for (Edge e : adj[v]) {
s.append(e + " ");
}
s.append(NEWLINE);
}
return s.toString();
}
答案 0 :(得分：1)
public EdgeWeightedGraph(In in) {
vertex = new ArrayList<Vertex>();
adj = (Bag<Edge>[]) new Bag[vertex.size()];
V = in.readInt();
E = in.readInt();
for (int j =0;j < V; j++){
int v = in.readInt();
double cost = in.readDouble();
Vertex u = new Vertex(v, cost);
vertex.add(u);
}
/* Snipped */
}
此构造函数未正确初始化adj。由于vertex.size()返回0，adj的大小为零。 V可能有一个不相关的值，因此您对错误的检查不会捕获它，抛出您看到的异常。我假设这是出了什么问题。