【发布时间】：2025-12-11 21:55:01
【问题描述】：
给定一个加权的、连通的、简单的无向图 G，每条边的权重只有 1 和 2
我想这样实现Prim's algorithm：
权重是 1 或 2，所以我可以简单地将边存储在 2 个单独的列表中，一个用于权重为 1 的边，第二个用于权重为 2 的边。
要找到权重最低的边，我只需从第一个列表中取一个，除非它是空的，在这种情况下，我从第二个列表中取一个边。
从列表中访问和删除元素是 O(1)，因此 Prim 的算法将在 O(V+E) 中运行。
package il.ac.oranim.alg2016;
import edu.princeton.cs.algs4.*;
public class MST12 {
private int weight; // weight of the tree
private Edge[] mstEdges; // use this to store the edges of your Minimum Spanning Tree
public MST12(EdgeWeightedGraph G, int s) throws IndexOutOfBoundsException, DisconnectedGraphException, WrongWeightException {
// check that the starting vertex is in the range 0,1,...,G.V()
if (s < 0 || s >= G.V()) {
throw new IndexOutOfBoundsException();
}
// check that the input graph is connected otherwise there is no (minimum) spanning tree
if (isConnected(G) == false) {
throw new DisconnectedGraphException();
}
// check that all the weights are 1 or 2
for (Edge e : G.edges()) {
if (e.weight() != 1 && e.weight() != 2) {
throw new WrongWeightException();
}
}
this.weight = 0; // make sure you update this value
// replace -->
// your code goes here
// <-- replace
}
// returns the weight of the tree
public int weight() {
return this.weight;
}
// checks whether a graph is connected
private static boolean isConnected(EdgeWeightedGraph G) {
// create a graph of class Graph with the same edges (weights)
Graph g = new Graph(G.V());
for (Edge e : G.edges()) {
int v = e.either();
g.addEdge(v, e.other(v));
}
// compute the connected components of the graph
CC cc = new CC(g);
// return true iff there is only one connected component
return cc.count() == 1;
}
/**
* Returns the edges in a minimum spanning tree as
* an iterable of edges
*/
public Iterable<Edge> edges() {
Queue<Edge> edges = new Queue<Edge>();
for (int i = 0; i < this.mstEdges.length; i++) {
Edge e = this.mstEdges[i];
int v = e.either();
edges.enqueue(new Edge(v, e.other(v), e.weight()));
}
return edges;
}
/**
* test the computing of an MST of a graph with weights 1 and 2 only
* the first argument is the name of the file that contains the graph (graph1.txt, graph2.txt, or graph3.txt)
* you can define this argument in Run.. --> (x)=Arguments
*/
public static void main(String[] args) {
In in = new In(args[0]);
EdgeWeightedGraph G = new EdgeWeightedGraph(in);
PrimMST primMST = new PrimMST(G);
MST12 mst12 = null;
try {
mst12 = new MST12(G,0);
}
catch (DisconnectedGraphException e) {
System.err.println("the input graph is not connected and hence has no (minimum) spanning tree");
}
catch (WrongWeightException e) {
System.err.println("not all weights in the input graph are 1 or 2");
}
System.out.println("Prim's MST weight = " + primMST.weight());
System.out.println("My MST's weight = " + mst12.weight());
}
}
我卡在
//replace-->//your code goes here//replace<--的部分
两个需要的类：
package il.ac.oranim.alg2016;
public class DisconnectedGraphException extends Exception {
public DisconnectedGraphException() {}
}
和
package il.ac.oranim.alg2016;
public class WrongWeightException extends Exception {
public WrongWeightException() {}
}
我也可以使用所有这些http://algs4.cs.princeton.edu/code/
有人可以帮我解决这部分吗
//replace-->//your code goes here//replace<--
我尝试将This 代码复制到//<--relpace,//replace--> 部分，然后将其从使用堆更改为两个列表。
Pseudocode of Prim's algorithm
换句话说，我需要代码：
【问题讨论】：
-
您的问题到底是什么？您是否尝试使用帖子中描述的两个列表来实施解决方案？如果是，出了什么问题？
标签： java eclipse algorithm graph minimum-spanning-tree