我目前正在尝试使用邻接列表来实现我自己的Dijkstra定制O（N.lgN）解决方案。现在，如果您熟悉此算法（很可能是您），我在为每个Vertex存储元组时遇到了问题。如果你不知道我在说什么，请联系：http://qr.ae/LoESY
使用
可以轻松地将元组存储在C ++中pair <int,int>.
无论如何，我找到了一个解决方案，并且不顾一切地知道，类似的类存在它被称为“抽象地图”。简单地说＆＃39;类。详情如下：
https://stackoverflow.com/a/11253710/4258892
现在您已经阅读了它，这与对＆lt;＆gt;对几乎相同并且足以将相邻边缘存储为密钥，并将权重存储为元组中的值。
声明：Map.Entry pair = new AbstractMap.SimpleEntry（1,2）;
现在我将所有输入以元组的形式存储在每个向量的ArrayList中。我计划将输入的源的元组添加到TreeSet中，并按权重的升序排序（对吗？）。但是，如果我只是将这些元组添加到TreeSet中，我会抛出一个错误：
Exception in thread "main" java.lang.ClassCastException:java.util.AbstractMap$SimpleEntry cannot be cast to java.lang.Comparable
现在我不知道如何为TreeSet实现自定义比较器，它会逐步对我的值进行排序（在Dijkstra中，权重最小的边缘会先出现吗？）。另外，如果TreeSet不可能，你能为我提供一个优先级队列并实现比较器吗？
即使您没有关注，也请查看我的代码。希望你能理解：
编辑代码根据以下建议编辑
package GRAPH;
import java.io.*;
import java.util.*;
/**
* Created by Shreyans on 3/25/2015 at 7:26 PM using IntelliJ IDEA (Fast IO Template)
*/
class DIJKSTA_TRY
{
public static void main(String[] args) throws Exception
{
InputReader in = new InputReader(System.in);
OutputWriter out = new OutputWriter(System.out);
//Initializing Graph
List<ArrayList<AbstractMap.SimpleEntry<Integer,Integer>>>gr=new ArrayList<ArrayList<AbstractMap.SimpleEntry<Integer, Integer>>>();//AbstractMap.SimpleEntry<Integer,Integer> is similar to pair<int a,int b> in C++
System.out.println("Enter no of Vertices");
int v=in.readInt();
System.out.println("Enter no of Edges");
int e=in.readInt();
for(int i=0;i<=v;i++)//Initializing rows for each vertex
{
gr.add(new ArrayList<AbstractMap.SimpleEntry<Integer, Integer>>());
}
System.out.println("Enter <Vertex> <Adjacent Vertex> <Weight>");
for(int i=0;i<e;i++)
{
int a = in.readInt();
int b = in.readInt();
int c = in.readInt();
gr.get(a).add(new AbstractMap.SimpleEntry<Integer, Integer>(b, c));
}
out.printLine(gr);
System.out.printf("Enter Source");
int s=in.readInt();
Comparator<AbstractMap.SimpleEntry<Integer, Integer>> comparator=new WeightComparator();
TreeSet<AbstractMap.SimpleEntry<Integer, Integer>>ts=new TreeSet<AbstractMap.SimpleEntry<Integer, Integer>>(comparator);
for(AbstractMap.SimpleEntry<Integer, Integer> pair: gr.get(s))//Error:Exception in thread "main" java.lang.ClassCastException: java.util.AbstractMap$SimpleEntry cannot be cast to java.lang.Comparable
{
ts.add(pair);
}
out.printLine(ts);
{
out.close();
}
}
static public class WeightComparator implements
Comparator<AbstractMap.SimpleEntry<Integer, Integer>>
{
@Override
public int compare(AbstractMap.SimpleEntry<Integer, Integer> one,
AbstractMap.SimpleEntry<Integer, Integer> two)
{
return Integer.compare(one.getValue(), two.getValue());
}
}
//FAST IO
private static class InputReader
{
private InputStream stream;
private byte[] buf = new byte[1024];
private int curChar;
private int numChars;
private SpaceCharFilter filter;
public InputReader(InputStream stream)
{
this.stream = stream;
}
public int read()
{
if (numChars == -1)
throw new InputMismatchException();
if (curChar >= numChars)
{
curChar = 0;
try
{
numChars = stream.read(buf);
} catch (IOException e)
{
throw new InputMismatchException();
}
if (numChars <= 0)
return -1;
}
return buf[curChar++];
}
public int readInt()
{
int c = read();
while (isSpaceChar(c))
c = read();
int sgn = 1;
if (c == '-')
{
sgn = -1;
c = read();
}
int res = 0;
do
{
if (c < '0' || c > '9')
throw new InputMismatchException();
res *= 10;
res += c - '0';
c = read();
} while (!isSpaceChar(c));
return res * sgn;
}
public String readString()
{
int c = read();
while (isSpaceChar(c))
c = read();
StringBuilder res = new StringBuilder();
do
{
res.appendCodePoint(c);
c = read();
} while (!isSpaceChar(c));
return res.toString();
}
public double readDouble()
{
int c = read();
while (isSpaceChar(c))
c = read();
int sgn = 1;
if (c == '-')
{
sgn = -1;
c = read();
}
double res = 0;
while (!isSpaceChar(c) && c != '.')
{
if (c == 'e' || c == 'E')
return res * Math.pow(10, readInt());
if (c < '0' || c > '9')
throw new InputMismatchException();
res *= 10;
res += c - '0';
c = read();
}
if (c == '.')
{
c = read();
double m = 1;
while (!isSpaceChar(c))
{
if (c == 'e' || c == 'E')
return res * Math.pow(10, readInt());
if (c < '0' || c > '9')
throw new InputMismatchException();
m /= 10;
res += (c - '0') * m;
c = read();
}
}
return res * sgn;
}
public long readLong()
{
int c = read();
while (isSpaceChar(c))
c = read();
int sgn = 1;
if (c == '-')
{
sgn = -1;
c = read();
}
long res = 0;
do
{
if (c < '0' || c > '9')
throw new InputMismatchException();
res *= 10;
res += c - '0';
c = read();
} while (!isSpaceChar(c));
return res * sgn;
}
public boolean isSpaceChar(int c)
{
if (filter != null)
return filter.isSpaceChar(c);
return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
}
public String next()
{
return readString();
}
public interface SpaceCharFilter
{
public boolean isSpaceChar(int ch);
}
}
private static class OutputWriter
{
private final PrintWriter writer;
public OutputWriter(OutputStream outputStream)
{
writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
}
public OutputWriter(Writer writer)
{
this.writer = new PrintWriter(writer);
}
public void print(Object... objects)
{
for (int i = 0; i < objects.length; i++)
{
if (i != 0)
writer.print(' ');
writer.print(objects[i]);
}
}
public void printLine(Object... objects)
{
print(objects);
writer.println();
}
public void close()
{
writer.close();
}
public void flush()
{
writer.flush();
}
}
}
Enter Source1
[[], [2=3, 4=3], [3=4], [1=7], [3=2]]
[2=3]
编辑有效。谢谢@rgettman
答案 0 :(得分：1)
您收到错误是因为AbstractMap.SimpleEntry班级没有实施Comparable。未TreeSet的{{1}}必须假设其元素为Comparator，但它们不是。
您确定需要创建Comparable，告诉Comparator如何订购元素，这是正确的。
创建自己的实现TreeSet的类。在Comparator<AbstractMap.SimpleEntry<Integer, Integer>>方法中，提取权重并进行比较。
compare