最小生成树-Kruskal算法 java代码实现

/* *日期:2010-04-18 20:02 *开发者:heroyan *联系方式:zndxysf@126.com *功能:无向图最小生成树Kruskal算法实现案例 */ import java.util.Scanner; import java.util.Arrays; import java.util.ArrayList; public class Kruskal{ 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 Kruskal(){} public static void main(String args[]){ Kruskal sp = new Kruskal(); 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; } } //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; } } } //prim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; int tag = 0; 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 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(){ 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); } } } class Edge { public int start;//始边 public int end;//终边 public double cost;//权重 }