BOJ-1922 네트워크 연결

MST 최소 스패닝트리를 찾는 기본 문제

 

https://www.acmicpc.net/problem/1922

1922번: 네트워크 연결

 

Kruscal 방식으로 MST를 구함.

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.StringTokenizer;

public class boj1922 {
    static int N, M;
    static Edge[] edges;
    static DJS djs;
    static class DJS {
        int[] mom;
        DJS(int n) {
            mom = new int[n+1];
            for (int i = 1; i <= n ; i++) mom[i] = i;
        }
        public int getMom(int n){
            if(n==mom[n]) return n;
            mom[n] = getMom(mom[n]);
            return mom[n];
        }
        public boolean isSame(int a, int b){
            return (getMom(a)==getMom(b));
        }
        public void union(int a, int b) {
            a = getMom(a);
            b = getMom(b);
            if(a==b) return;
            mom[b] = a;
        }
    }
    static class Edge implements Comparable<Edge> {
        int s, e, v;
        Edge(int s, int e, int v) {
            this.s = s;
            this.e = e;
            this.v = v;
        }

        @Override
        public int compareTo(Edge o) {
            return this.v - o.v;
        }
    }
    public static void main(String[] args) throws IOException {
        System.setIn(new FileInputStream("res/boj_1922.txt"));
        long Start = System.currentTimeMillis();
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        N = Integer.parseInt(br.readLine());
        M = Integer.parseInt(br.readLine());
        edges = new Edge[M];
        djs = new DJS(N);
        StringTokenizer st;
        int a, b, c;
        for (int i = 1; i <= M ; i++) {
            st = new StringTokenizer(br.readLine(), " ");
            a = Integer.parseInt(st.nextToken());
            b = Integer.parseInt(st.nextToken());
            c = Integer.parseInt(st.nextToken());

            edges[i-1] = new Edge(a, b, c);
        }

        Arrays.sort(edges);

        Edge ed;
        long result = 0;
        for (int i = 0; i < M ; i++) {
            ed = edges[i];
            if(!djs.isSame(ed.s, ed.e)) {
                djs.union(ed.s,ed.e);
                result += ed.v;
            }
        }

        System.out.println(result);
    }
}