我正在尝试计算保存在文本文件中的加权连接图的MST。但是，我得到一个例外：ArrayIndexOutOfBounds: 1
我知道我遇到了问题而我正在尝试访问无效的数组索引。我似乎无法找到改变的地点和内容。我在这个网站和其他网站上搜索了一些类似的问题，但无济于事。 如果有人能够指出我出错的地方，我们将不胜感激。
class Heap
{
private int[] h; // heap array
private int[] hPos; // hPos[h[k]] == k
private int[] dist; // dist[v] = priority of v
private int N; // heap size
// The heap constructor gets passed from the Graph:
// 1. maximum heap size
// 2. reference to the dist[] array
// 3. reference to the hPos[] array
public Heap(int maxSize, int[] _dist, int[] _hPos)
{
N = 0;
h = new int[maxSize + 1];
dist = _dist;
hPos = _hPos;
}
public boolean isEmpty()
{
return N == 0;
}
public void siftUp( int k)
{
int v = h[k];
h[0] = 0; //puts dummy node at top of the heap
dist[0] = Integer.MIN_VALUE;
while (dist[v] < dist[h[k / 2]])
{
h[k] = h[k / 2];
hPos[h[k]] = k;
k = k / 2;
}
h[k] = v;
hPos[v] = k;
}
public void siftDown(int k)
{
int v, j;
v = h[k];
j = 2 * k;
while (j <= N)
{
//Ensures there is something in the Heap, then finds the larger branch
if (j + 1 <= N && dist[h[j]] > dist[h[j + 1]])
{
j++;
}
//comparing the position with the node being moved
if (dist[h[j]] >= dist[v])
{
break;
}
h[k] = h[j];
k = j;
j = k * 2;
}
h[k] = v;
hPos[v] = k;
}
public void insert( int x)
{
h[++N] = x;
siftUp( N);
}
public int remove()
{
int v = h[1];
hPos[v] = 0; // v is no longer in heap
h[N+1] = 0; // put null node into empty spot
h[1] = h[N--];
siftDown(1);
return v;
}
}
class Graph {
class Node {
public int vert;
public int wgt;
public int data;
public Node next;
}
// V = number of vertices
// E = number of edges
// adj[] is the adjacency lists array
private int V, E;
private Node[] adj;
private Node z;
private int[] mst;
// used for traversing graph
private int[] visited;
private int id;
// default constructor
public Graph(String graphFile) throws IOException
{
int u, v;
int e, wgt;
Node t;
FileReader fr = new FileReader(graphFile);
BufferedReader reader = new BufferedReader(fr);
String splits = " +"; // multiple whitespace as delimiter
String line = reader.readLine();
String[] parts = line.split(splits);
System.out.println("Parts[] = " + parts[0] + " " + parts[1]);
V = Integer.parseInt(parts[0]);
E = Integer.parseInt(parts[1]);
// create sentinel node
z = new Node();
z.next = z;
// create adjacency lists, initialised to sentinel node z
adj = new Node[V+1];
for(v = 1; v <= V; ++v)
{
adj[v] = z;
}
// read the edges
System.out.println("Reading edges from text file");
for(e = 1; e <= E; ++e)
{
line = reader.readLine();
parts = line.split(splits);
u = Integer.parseInt(parts[0]);
v = Integer.parseInt(parts[1]);
wgt = Integer.parseInt(parts[2]);
System.out.printf("Edge %1$s--(%2$s)--%3$s" + "\r\n", toChar(u), wgt, toChar(v));
// write code to put edge into adjacency matrix
t = new Node();
t.data = wgt;
t.vert = u;
t.next = adj[v];
adj[v] = t;
t = new Node();
t.data = wgt;
t.vert = v;
t.next = adj[u];
adj[u] = t;
}
}
// convert vertex into char for pretty printing
private char toChar(int u)
{
return (char)(u + 64);
}
// method to display the graph representation
public void display() {
int v;
Node n;
for(v=1; v<=V; ++v){
System.out.print("\nadj[" + toChar(v) + "] ->" );
for(n = adj[v]; n != z; n = n.next)
System.out.print(" |" + toChar(n.vert) + " | " + n.wgt + "| ->");
}
System.out.println("");
}
public void MST_Prim(int s)
{
int v, u;
int wgt, wgt_sum = 0;
int[] dist, parent, hPos;
Node t;
//the distance from node to node
dist = new int[V + 1];
//the parent node
parent = new int[V + 1];
//current heap position
hPos = new int[V + 1];
// initialising parent and position to zero, and dist to the max value
for (v = 1; v <= V; v++)
{
dist[v] = Integer.MAX_VALUE;
parent[v] = 0;
hPos[v] = 0;
}
Heap heap = new Heap(V + 1, dist, hPos);
heap.insert(s);
dist[s] = 0;
for(v = 0; v<dist[v]; v++)
{
dist[v] = dist[v];
parent[v] = 0;
hPos[v] = 0;
}
dist[s] = 0;
Heap pq = new Heap(V, dist, hPos);
pq.insert(s);
while (!heap.isEmpty())
{
v = heap.remove();
System.out.printf("\nAdding edge {0}--({1})--{2}", toChar(parent[v]), dist[v], toChar(v));
//calculates the sum of the weights
wgt_sum += dist[v];
//prevents duplicates
dist[v] = -dist[v];
for (t = adj[v]; t != z; t = t.next)
{
if (t.data < dist[t.vert])
{
dist[t.vert] = t.data;
parent[t.vert] = v;
//If the vertex is empty, insert next vertex
if (hPos[t.vert] == 0)
{
heap.insert(t.vert);
}
else //Else call sift up
{
heap.siftUp(hPos[t.vert]);
}
}
}
}
System.out.print("\n\nWeight of MST = " + wgt_sum + "\n");
mst = parent;
}
public void showMST()
{
System.out.println("Minimum Spanning tree parent array is:");
for(int v = 1; v <= V; ++v)
{
System.out.println(toChar(v) + " -> " + toChar(mst[v]));
}
System.out.println("");
}
}
public class PrimLists {
public static void main(String[] args) throws IOException
{
int s = 2;
String fname = "wGraph3.txt";
Graph g = new Graph(fname);
g.display();
}
}
似乎在这两条线上发生例外，但我看不出它们有什么问题。
System.out.println("Parts[] = " + parts[0] + " " + parts[1]);
Graph g = new Graph(fname);
文件wGraph3.txt的内容如下
7 11
1 2 7
1 4 5
2 3 8
2 4 9
2 5 7
3 5 5
4 5 15
4 6 6
5 6 8
5 7 9
6 7 11
这种格式对我来说似乎很好，我一直在这方面工作，我只是没有看到问题。