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带权图

1.1带权图的实现

在无向无权图的基础上，增加边的权。

使用TreeMap存储边的权重。

• 遍历输入文件，创建TreeMap adj存储每个节点。
• 每个输入的adj节点链接新的TreeMap，存储相邻的边和权重

private TreeMap<Integer, Integer>[] adj;adj = new TreeMap[V];for(int i = 0; i < V; i ++)adj[i] = new TreeMap<Integer, Integer>();

• 两条边相连，则分别把权重加入各自的邻接表中

adj[a].put(b, weight);
adj[b].put(a, weight);

• 判断两点之间是否有边

public boolean hasEdge(int v, int w){validateVertex(v);validateVertex(w);return adj[v].containsKey(w);
}

• 求相邻的所有节点

public Iterable<Integer> adj(int v){validateVertex(v);return adj[v].keySet();
}

• 求两点的权值

public int getWeight(int v, int w){if(hasEdge(v, w)) return adj[v].get(w);throw new IllegalArgumentException(String.format("No edge %d-%d", v, w));
}

• 移除边

public void removeEdge(int v, int w){validateVertex(v);validateVertex(w);if(adj[v].containsKey(w)) E --;adj[v].remove(w);adj[w].remove(v);
}

• 复制一个图

public Object clone(){try{WeightedGraph cloned = (WeightedGraph) super.clone();cloned.adj = new TreeMap[V];for(int v = 0; v < V; v ++){cloned.adj[v] = new TreeMap<Integer, Integer>();for(Map.Entry<Integer, Integer> entry: adj[v].entrySet())cloned.adj[v].put(entry.getKey(), entry.getValue());}return cloned;}catch (CloneNotSupportedException e){e.printStackTrace();}return null;
}

1.2 完整代码

package Chapter09_Weight_Graph;import java.io.File;
import java.io.IOException;
import java.util.Map;
import java.util.TreeMap;
import java.util.Scanner;/// 暂时只支持无向带权图
public class WeightedGraph implements Cloneable{private int V;private int E;private TreeMap<Integer, Integer>[] adj;public WeightedGraph(String filename){File file = new File(filename);try(Scanner scanner = new Scanner(file)){V = scanner.nextInt();if(V < 0) throw new IllegalArgumentException("V must be non-negative");adj = new TreeMap[V];for(int i = 0; i < V; i ++)adj[i] = new TreeMap<Integer, Integer>();E = scanner.nextInt();if(E < 0) throw new IllegalArgumentException("E must be non-negative");for(int i = 0; i < E; i ++){int a = scanner.nextInt();validateVertex(a);int b = scanner.nextInt();validateVertex(b);int weight = scanner.nextInt();if(a == b) throw new IllegalArgumentException("Self Loop is Detected!");if(adj[a].containsKey(b)) throw new IllegalArgumentException("Parallel Edges are Detected!");adj[a].put(b, weight);adj[b].put(a, weight);}}catch(IOException e){e.printStackTrace();}}public void validateVertex(int v){if(v < 0 || v >= V)throw new IllegalArgumentException("vertex " + v + "is invalid");}public int V(){return V;}public int E(){return E;}public boolean hasEdge(int v, int w){validateVertex(v);validateVertex(w);return adj[v].containsKey(w);}public Iterable<Integer> adj(int v){validateVertex(v);return adj[v].keySet();}public int getWeight(int v, int w){if(hasEdge(v, w)) return adj[v].get(w);throw new IllegalArgumentException(String.format("No edge %d-%d", v, w));}public int degree(int v){validateVertex(v);return adj[v].size();}public void removeEdge(int v, int w){validateVertex(v);validateVertex(w);if(adj[v].containsKey(w)) E --;adj[v].remove(w);adj[w].remove(v);}@Overridepublic Object clone(){try{WeightedGraph cloned = (WeightedGraph) super.clone();cloned.adj = new TreeMap[V];for(int v = 0; v < V; v ++){cloned.adj[v] = new TreeMap<Integer, Integer>();for(Map.Entry<Integer, Integer> entry: adj[v].entrySet())cloned.adj[v].put(entry.getKey(), entry.getValue());}return cloned;}catch (CloneNotSupportedException e){e.printStackTrace();}return null;}@Overridepublic String toString(){StringBuilder sb = new StringBuilder();sb.append(String.format("V = %d, E = %d\n", V, E));for(int v = 0; v < V; v ++){sb.append(String.format("%d : ", v));for(Map.Entry<Integer, Integer> entry: adj[v].entrySet())sb.append(String.format("(%d: %d) ", entry.getKey(), entry.getValue()));sb.append('\n');}return sb.toString();}public static void main(String[] args){WeightedGraph g = new WeightedGraph("gw1.txt");System.out.print(g);}
}