最小生成树-Prim算法 java代码实现

/*
*日期:2010-04-18 11:37
*开发者:heroyan
*联系方式:zndxysf@126.com
*功能:无向图最小生成树Prim算法实现案例
*/
import java.util.Scanner;
import java.util.Arrays;
import java.util.ArrayList;

public class SpanningTree{
private static int MAX = 100;
private double cost[][] = new double[MAX][MAX];
private ArrayList<Edge> edge = new ArrayList<Edge>();
private int[] near = new int[MAX];
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 SpanningTree(){}

public static void main(String args[]){
SpanningTree sp = new SpanningTree();
sp.init();
sp.prim();
sp.print();
}
//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();
//二维数组的填充要注意
for(int i = 0; i < MAX; ++i){
Arrays.fill(cost[i],INFINITY);
}
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;
}
cost[p][q] = w;
cost[q][p] = w;
}

Edge tmp = getMinCostEdge();
edge.add(tmp);
p = tmp.start;
q = tmp.end;
mincost = cost[p][q];

for(int i = 1; i <= n; ++i){
if(cost[i][p] < cost[i][q]){
near[i] = p;
}else{
near[i] = q;
}
}
near[p] = near[q] = 0;
}
//寻找最小成本的边
public Edge getMinCostEdge(){
Edge tmp = new Edge();
double min = INFINITY;

for(int i = 1; i < n; ++i){
for(int j = i+1; j <= n; ++j){
if(cost[i][j] < min){
min = cost[i][j];
tmp.start = i;
tmp.end = j;
}
}
}
//System.out.println(min);
return tmp;
}
//prim算法主体
public void prim(){
//找剩下的n-2条边
for(int i = 2; i < n; ++i){
double min = INFINITY;
Edge tmp = new Edge();
for(int j = 1; j <= n; ++j){
if(near[j] != 0 && cost[j][near[j]] < min){
tmp.start = j;
tmp.end = near[j];
min = cost[j][near[j]];
}
}
mincost += cost[tmp.start][tmp.end];
edge.add(tmp);
near[tmp.start] = 0;
for(int k = 1; k <= n; ++k){
if(near[k] != 0 && cost[k][near[k]] > cost[k][tmp.start]){
near[k] = tmp.start;
}
}
}
if(mincost >= INFINITY){
System.out.println("no spanning tree");
}
}
//打印结果
public void print(){
for(int i = 0; i < edge.size(); ++i){
Edge e = edge.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
}