POJ2349最小生成树

最小生成树中第S长的边是使得联通分支数<=S的最小的D。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.StringTokenizer;

public class Main {
public static void main(String[] args) {
new POJ2349().solve();
}
}

class POJ2349 {

InputReader in = new InputReader(System.in);
PrintWriter out = new PrintWriter(System.out);
double[] x , y ;
int[] father ;
List<Edge> edges ;
int S , P ;

double dist(int i , int j){
return Math.sqrt((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j])) ;
}

int getFather(int u){
return u == father[u] ? u : getFather(father[u]) ;
}

boolean canUnion(int u , int v){
int fu = getFather(u) ;
int fv = getFather(v) ;
if(fu == fv) return false ;
father[fu] = fv ;
return true ;
}

double kruskal(){
double res = 0 ;
father = new int[P] ;
for(int i = 0 ; i < P ; i++) father[i] = i ;
int size = 0 ;
Collections.sort(edges) ;
for(Edge e : edges){
if(canUnion(e.start , e.end)){
e.used = true ;
if(++size >= P) break ;
}
}
Collections.reverse(edges) ;
for(Edge e : edges){
if(e.used){
if(--S == 0){
res = e.length ;
break ;
}
}
}

return res ;
}

void solve() {
int t = in.nextInt() ;
while(t-- > 0){
S = in.nextInt() ;
P = in.nextInt() ;
x = new double[P] ;
y = new double[P] ;
for(int i = 0 ; i < P ; i++){
x[i] = in.nextDouble() ;
y[i] = in.nextDouble() ;
}
edges = new ArrayList<Edge>() ;
for(int i = 0 ; i < P ; i++){
for(int j = 0 ; j < i ; j++){
edges.add(new Edge(i, j, dist(i,j) ) ) ;
}
}
out.printf("%.2f\n" , kruskal() );
}

out.flush();
}

class Edge implements Comparable<Edge>{
int start ;
int end ;
double length ;
boolean used ;
Edge(int start , int end , double length){
this.start = start ;
this.end = end ;
this.length = length ;
used = false ;
}
@Override
public int compareTo(Edge other) {
return Double.compare(length , other.length) ;
}
}

}

class InputReader {
public BufferedReader reader;
public StringTokenizer tokenizer;

public InputReader(InputStream stream) {
reader = new BufferedReader(new InputStreamReader(stream), 32768);
tokenizer = null;
}

public String next() {
while (tokenizer == null || !tokenizer.hasMoreTokens()) {
try {
tokenizer = new StringTokenizer(reader.readLine());
} catch (IOException e) {
throw new RuntimeException(e);
}
}
return tokenizer.nextToken();
}

public int nextInt() {
return Integer.parseInt(next());
}

public long nextLong() {
return Long.parseLong(next());
}

public double nextDouble() {
return Double.parseDouble(next());
}

}