304 lines
8.8 KiB
Java
304 lines
8.8 KiB
Java
/*This is a java program to find global min cut of the graph. In computer science and graph theory, Karger’s algorithm is a randomized algorithm to compute a minimum cut of a connected graph.*/
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import java.io.BufferedReader;
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import java.io.FileReader;
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import java.util.ArrayList;
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import java.util.Comparator;
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import java.util.HashSet;
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import java.util.Iterator;
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import java.util.LinkedHashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.Random;
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import java.util.Set;
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import java.util.TreeMap;
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public class GlobalMinCut
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{
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private static class Graph
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{
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private final Map<Integer, Vertex> vertices = new TreeMap<Integer, Vertex>(
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new Comparator<Integer>()
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{
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@Override
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public int compare(Integer arg0, Integer arg1)
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{
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return arg0.compareTo(arg1);
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}
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});
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private final List<Edge> edges = new ArrayList<Edge>();
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public void addVertex(Vertex v)
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{
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vertices.put(v.lbl, v);
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}
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public Vertex getVertex(int lbl)
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{
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Vertex v;
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if ((v = vertices.get(lbl)) == null)
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{
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v = new Vertex(lbl);
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addVertex(v);
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}
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return v;
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}
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}
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private static class Vertex
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{
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private final int lbl;
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private final Set<Edge> edges = new HashSet<Edge>();
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public Vertex(int lbl)
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{
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this.lbl = lbl;
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}
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public void addEdge(Edge edge)
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{
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edges.add(edge);
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}
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public Edge getEdgeTo(Vertex v2)
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{
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for (Edge edge : edges)
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{
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if (edge.contains(this, v2))
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return edge;
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}
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return null;
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}
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}
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private static class Edge
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{
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private final List<Vertex> ends = new ArrayList<Vertex>();
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public Edge(Vertex fst, Vertex snd)
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{
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if (fst == null || snd == null)
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{
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throw new IllegalArgumentException("Both vertices are required");
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}
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ends.add(fst);
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ends.add(snd);
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}
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public boolean contains(Vertex v1, Vertex v2)
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{
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return ends.contains(v1) && ends.contains(v2);
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}
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public Vertex getOppositeVertex(Vertex v)
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{
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if (!ends.contains(v))
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{
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throw new IllegalArgumentException("Vertex " + v.lbl);
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}
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return ends.get(1 - ends.indexOf(v));
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}
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public void replaceVertex(Vertex oldV, Vertex newV)
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{
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if (!ends.contains(oldV))
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{
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throw new IllegalArgumentException("Vertex " + oldV.lbl);
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}
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ends.remove(oldV);
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ends.add(newV);
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}
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}
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public static int minCut(Graph gr)
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{
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Random rnd = new Random();
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while (gr.vertices.size() > 2)
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{
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Edge edge = gr.edges.remove(rnd.nextInt(gr.edges.size()));
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Vertex v1 = cleanVertex(gr, edge.ends.get(0), edge);
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Vertex v2 = cleanVertex(gr, edge.ends.get(1), edge);
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// contract
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Vertex mergedVertex = new Vertex(v1.lbl);
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redirectEdges(gr, v1, mergedVertex);
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redirectEdges(gr, v2, mergedVertex);
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gr.addVertex(mergedVertex);
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}
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return gr.edges.size();
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}
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private static Vertex cleanVertex(Graph gr, Vertex v, Edge e)
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{
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gr.vertices.remove(v.lbl);
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v.edges.remove(e);
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return v;
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}
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private static void redirectEdges(Graph gr, Vertex fromV, Vertex toV)
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{
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for (Iterator<Edge> it = fromV.edges.iterator(); it.hasNext();)
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{
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Edge edge = it.next();
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it.remove();
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if (edge.getOppositeVertex(fromV) == toV)
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{
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// remove self-loop
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toV.edges.remove(edge);
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gr.edges.remove(edge);
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}
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else
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{
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edge.replaceVertex(fromV, toV);
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toV.addEdge(edge);
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}
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}
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}
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public static int[][] getArray(String relPath)
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{
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Map<Integer, List<Integer>> vertices = new LinkedHashMap<Integer, List<Integer>>();
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FileReader fr;
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try
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{
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fr = new FileReader(relPath);
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BufferedReader br = new BufferedReader(fr);
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String line;
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while ((line = br.readLine()) != null)
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{
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String[] split = line.trim().split("(\\s)+");
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List<Integer> adjList = new ArrayList<Integer>();
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for (int i = 1; i < split.length; i++)
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{
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adjList.add(Integer.parseInt(split[i]) - 1);
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}
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vertices.put(Integer.parseInt(split[0]) - 1, adjList);
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}
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fr.close();
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}
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catch (Exception e)
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{
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e.printStackTrace();
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}
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int[][] array = new int[vertices.size()][];
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for (Map.Entry<Integer, List<Integer>> entry : vertices.entrySet())
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{
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List<Integer> adjList = entry.getValue();
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int[] adj = new int[adjList.size()];
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for (int i = 0; i < adj.length; i++)
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{
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adj[i] = adjList.get(i);
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}
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array[entry.getKey()] = adj;
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}
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return array;
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}
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private static Graph createGraph(int[][] array)
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{
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Graph gr = new Graph();
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for (int i = 0; i < array.length; i++)
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{
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Vertex v = gr.getVertex(i);
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for (int edgeTo : array[i])
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{
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Vertex v2 = gr.getVertex(edgeTo);
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Edge e;
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if ((e = v2.getEdgeTo(v)) == null)
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{
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e = new Edge(v, v2);
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gr.edges.add(e);
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v.addEdge(e);
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v2.addEdge(e);
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}
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}
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}
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return gr;
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}
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/**
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* @param args
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*/
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public static void main(String[] args)
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{
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int[][] arr = getArray("GlobalMinCut.txt");
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Map<Integer, Integer> statistics = new LinkedHashMap<Integer, Integer>();
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int min = arr.length;
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int iter = arr.length * arr.length;
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Graph g = createGraph(arr);
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printGraph(g);
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for (int i = 0; i < iter; i++)
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{
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Graph gr = createGraph(arr);
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int currMin = minCut(gr);
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min = Math.min(min, currMin);
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Integer counter;
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if ((counter = statistics.get(currMin)) == null)
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{
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counter = 0;
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}
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statistics.put(currMin, counter + 1);
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}
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System.out.println("Min: " + min + " stat: "
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+ (statistics.get(min) * 100 / iter) + "%");
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}
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private static void printGraph(Graph gr)
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{
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System.out.println("Printing graph");
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for (Vertex v : gr.vertices.values())
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{
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System.out.print(v.lbl + ":");
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for (Edge edge : v.edges)
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{
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System.out.print(" " + edge.getOppositeVertex(v).lbl);
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}
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System.out.println();
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}
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}
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}
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/*
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Printing graph
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0: 35 38 17 18 14 22
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1: 35 8 17 3 25 22
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2: 34 15 5 10
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3: 23 1 17 22
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4: 7 20 13 28
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5: 2 33 15 34
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6: 32 27 37 29
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7: 13 11 30 4 28
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8: 38 16 12 1 9 19
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9: 28 8 11 13 19
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10: 15 32 2 25 29
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11: 19 13 7 9
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12: 8 23 38 19
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13: 11 7 9 4
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14: 18 35 25 0
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15: 34 31 2 10 29 16 5
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16: 8 15 39 37 27 31
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17: 0 38 23 1 3
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18: 14 25 0 26
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19: 11 12 8 9
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20: 28 4 24 36
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21: 31 33 39 34
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22: 35 0 1 3
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23: 3 17 12 38
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24: 30 28 36 20
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25: 26 18 14 10 1 30
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26: 25 36 28 30 18
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27: 31 6 37 16
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28: 9 26 20 24 7 4
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29: 36 15 32 6 10
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30: 7 24 26 25 36
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31: 15 21 27 39 16
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32: 6 10 29 37
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33: 21 5 39 34
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34: 15 2 21 5 33
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35: 0 1 14 22
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36: 29 26 24 30 20
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37: 39 16 6 27 32
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38: 0 8 17 12 23
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39: 37 31 21 16 33
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Min: 3 stat: 6% |