Kruskal和Prim最小生成树java实现

Kruskal最小生成树

//思路参考http://blog.csdn.net/luomingjun12315/article/details/47700237
import java.util.Scanner;  
import java.util.Arrays;  
import java.util.ArrayList;  
  
public class KruskalMST {  
    private static int MAX = 100;  
    private ArrayList<Edge> edge = new ArrayList<Edge>();//整个图的边  
    private ArrayList<Edge> target = new ArrayList<Edge>();//目标边,最小生成树  
    private int[] parent = new int[MAX];//标志所在的集合  
    private static double INFINITY = 99999999.99;//定义无穷大  
    private double mincost = 0.0;//最小成本  
    private int n;//结点个数  

    public static void main(String args[]){  
        KruskalMST sp = new KruskalMST();  
        sp.init();  
        sp.kruskal();  
        sp.print();  
    }  
    //初始化  
    public void init(){  
        Scanner scan = new Scanner(System.in);  
        int p,q;  
        double w;  
          
        System.out.println("spanning tree begin!Input the node number:");  
        n = scan.nextInt();  
        System.out.println("Input the graph(-1,-1,-1 to exit)");  
          
        while(true){  
            p = scan.nextInt();  
            q = scan.nextInt();  
            w = scan.nextDouble();  
            if(p < 0 || q < 0 || w < 0){  
                break;  
            }  
            Edge e = new Edge();  
            e.start = p;  
            e.end = q;  
            e.cost = w;  
            edge.add(e);  
        }  
          
        mincost = 0.0;  
          
        for (int i = 1; i <= n; ++i){  
            parent[i] = i;  
        }  
        scan.close();
    }  
    //集合合并  
    public void union(int j, int k){  
        for(int i = 1; i <= n; ++i){  
            if(parent[i] == j){  
                parent[i] = k;  
            }  
        }  
    }  
    //Kruskal算法主体  
    public void kruskal(){  
        //找剩下的n-2条边  
        int i = 0;  
        while(i < n-1 && edge.size() > 0){  
            //每次取一最小边,并删除  
            double min = INFINITY;  
            Edge tmp = null;  
            for(int j = 0; j < edge.size(); ++j){  
                Edge tt = edge.get(j);  
                if(tt.cost < min){  
                    min = tt.cost;  
                    tmp = tt;  
                }  
            }  
            int jj = parent[tmp.start];  
            int kk = parent[tmp.end];  
            //去掉环,判断当前这条边的两个端点是否属于同一棵树
            if(jj != kk){  
                ++i;  
                target.add(tmp);  
                mincost += tmp.cost;  
                union(jj,kk);  
            }  
            edge.remove(tmp);  
        }  
        if(i != n-1){  
            System.out.println("no spanning tree");  
        }  
    }  
    //打印结果  
    public void print(){  
        double sum = 0;
        for(int i = 0; i < target.size(); ++i){  
            Edge e = target.get(i);  
            System.out.println("the " + (i+1) + "th edge:" + e.start + "---" + e.end + "   cost:" + e.cost);  
            sum += e.cost;
        }  
        System.out.println("the MST cost:"+sum);
    }  
}  
  
class Edge  
{  
    public int start;//始边  
    public int end;//终边  
    public double cost;//权重  
}  

Prim最小生成树

//思路参考http://blog.csdn.net/yeruby/article/details/38615045
import java.util.Scanner;

public class PrimMST {
    private static int MAX = 100;
    private static int[][] graph = new int[MAX][MAX];
    private int[] lowcost = new int[MAX];// 标志所在的集合
    private int[] mst = new int[MAX];//
    private static int INFINITY = 99999999;// 定义无穷大
    private int mincost = 0;// 最小成本
    private static int mstcost = 0;// 最小成本
    private static int n;// 结点个数
    private int middle;// 中间结点
    private int sum = 0;

    public static void main(String args[]) {
        PrimMST sp = new PrimMST();
        sp.init();
        mstcost = sp.prim(graph, n);
        System.out.println("最小生成树权值和为:" + mstcost);
    }

    // 初始化
    public void init() {
        Scanner scan = new Scanner(System.in);
        int p, q, w;
        System.out.println("spanning tree begin!Input the node number:");
        n = scan.nextInt();
        System.out.println("Input the graph(-1,-1,-1 to exit)");
        while (true) {
            p = scan.nextInt();
            q = scan.nextInt();
            w = scan.nextInt();
            if (p < 0 || q < 0 || w < 0) {
                break;
            }
            graph[p][q] = w;
            graph[q][p] = w;
        }
        scan.close();
    }

    // prim算法主体
    public int prim(int graph[][], int n) {
        for (int i = 2; i <= n; i++) {
            lowcost[i] = graph[1][i];
            mst[i] = 1;
        }
        mst[1] = 0;
        for (int i = 2; i <= n; i++) {
            mincost = INFINITY;
            middle = 0;
            for (int j = 0; j <= n; j++) {
                if (lowcost[j] < mincost && lowcost[j] != 0) {
                    mincost = lowcost[j];
                    middle = j;
                }
            }
            System.out.println(mst[middle] + "--" + middle + "==" + mincost);
            sum += mincost;
            lowcost[middle] = 0;
            for (int j = 0; j <= n; j++) {
                if (graph[middle][j] < lowcost[j]) {
                    lowcost[j] = graph[middle][j];
                    mst[j] = middle;
                }
            }
        }
        return sum;
    }
}

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