JAVA CCF-201812-4 数据中心

欢迎访问我的CCF认证解题目录

题目描述

思路过程

题目写得比较复杂，其实就是求最小生成树的最大边，直接套最小生成树的模板修改一下即可

代码

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Comparator;
import java.util.PriorityQueue;

public class Main {
	
	public static int[] father = new int[500005];
	
	//采用克鲁斯卡尔算法，求最小生成树的最大边
	public static void main(String[] args) throws NumberFormatException, IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(br.readLine()), m = Integer.parseInt(br.readLine());
		int root = Integer.parseInt(br.readLine()), count = 0, max = 0;	//计数和最大边
		PriorityQueue<Edge> edges = new PriorityQueue<Edge>(new Comparator<Edge>() {
			@Override
			public int compare(Edge o1, Edge o2) {
				return o1.time - o2.time;//按time升序
			}
		});
		
		for ( int i = 1; i < n+1; i++ ) father[i] = i;
		for ( int i = 0; i < m; i++ ) {
			String[] line = br.readLine().split(" ");
			edges.offer(new Edge(Integer.parseInt(line[0]), Integer.parseInt(line[1]), Integer.parseInt(line[2])));
		}
		
		while ( !edges.isEmpty() ) {
			Edge e = edges.poll();
			int father1 = findFather(e.v1), father2 = findFather(e.v2);
			if ( father1 != father2 ) {
				father[father1] = father2;
				if ( e.time > max ) max = e.time;
				if ( ++count == n-1 ) break;//以连接所有边
			}
		}
		
		System.out.println(max);
	}
	
	//路径压缩
	public static int findFather( int index ) {
		if ( father[index] == index ) return index;
		else {
			int temp = findFather(father[index]);
			father[index] = temp;
			return temp;
		}
	}
}
class Edge {//存储边
	int v1,v2,time;
	public Edge(int v1, int v2, int time) {
		this.v1 = v1;
		this.v2 = v2;
		this.time = time;
	}
}