kruskal

iScript · iScript · commit 9044a7f37c09 · 2020-02-15T23:21:11.000+08:00
diff --git a/.idea/workspace.xml b/.idea/workspace.xml
diff --git a/src/Kruskal.java b/src/Kruskal.java
@@ -0,0 +1,51 @@
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class Kruskal {
+    private WeightedGraph G;
+    private ArrayList<WeightedEdge> mst;
+
+    public Kruskal(WeightedGraph G){
+        this.G = G;
+        mst = new ArrayList<WeightedEdge>();
+
+        // 需要判断联通
+
+        // Kruskal
+        ArrayList<WeightedEdge> edges = new ArrayList<>();
+        for(int v = 0;v<G.V();v++){
+            for(int w : G.adj(v)){
+                if(v < w){//避免重复
+                    //将边都加入
+                    edges.add(new WeightedEdge(v,w,G.getWeight(v,w)));
+                }
+            }
+        }
+
+        // 排序 从小到大
+        Collections.sort(edges);
+
+        // 使用并查集判断是否形成环，若形成环在集合中顶点会有重复
+        UF uf = new UF(G.V());
+        for(WeightedEdge edge: edges){
+            int v = edge.getV();
+            int w = edge.getW();
+            if(!uf.isConnected(v, w)){  // v w 是否在一个集合中
+                mst.add(edge);
+                uf.unionElements(v, w); // 合并
+            }
+        }
+
+    }
+
+    public ArrayList<WeightedEdge> result(){
+        return mst;
+    }
+
+    public static void main(String[] args){
+
+        WeightedGraph g = new WeightedGraph("g.txt");
+        Kruskal kruskal = new Kruskal(g);
+        System.out.println(kruskal.result());
+    }
+}
diff --git a/src/UF.java b/src/UF.java
@@ -0,0 +1,33 @@
+//并查集
+public class UF{
+
+    private int[] parent;
+
+    public UF(int n){
+
+        parent = new int[n];
+        for(int i = 0 ; i < n ; i ++)
+            parent[i] = i;
+    }
+
+    public int find(int p){
+        if( p != parent[p] )
+            parent[p] = find( parent[p] );
+        return parent[p];
+    }
+
+    public boolean isConnected(int p , int q){
+        return find(p) == find(q);
+    }
+
+    public void unionElements(int p, int q){
+
+        int pRoot = find(p);
+        int qRoot = find(q);
+
+        if( pRoot == qRoot )
+            return;
+
+        parent[pRoot] = qRoot;
+    }
+}
diff --git a/src/WeightedEdge.java b/src/WeightedEdge.java
@@ -0,0 +1,30 @@
+public class WeightedEdge implements Comparable<WeightedEdge>{
+
+
+    private int v, w, weight;
+
+    public WeightedEdge(int v, int w , int weight){
+        this.v = v;
+        this.w = w;
+        this.weight = weight;
+
+
+    }
+
+    public int getV(){return v;}
+
+    public int getW(){return w;}
+
+    @Override
+    public int compareTo(WeightedEdge another){
+        return weight - another.weight;
+    }
+
+    @Override
+    public String toString(){
+        return String.format("(%d-%d : %d)", v, w,weight);
+    }
+
+
+
+}
