19914 最小生成树2

19914 最小生成树2

⭐️难度：中等
🌟考点：最小生成树
📖

📚

import java.util.*;

public class Main {
    static class Edge{
        int u,v,w;
        Edge(int u,int v,int w){
            this.u = u;
            this.v = v;
            this.w = w;
        }
    }

    static ArrayList<Edge> g = new ArrayList<>(); // 存边
    static int n;
    static int m;
    static class UnionSet{  // 并查集
        int[] f,sz;
        UnionSet(int n){
            f = new int[n+1];
            sz = new int[n+1];
            for (int i = 1; i <= n; i++) {
                f[i] = i;
                sz[i] = i;
            }
        }

        int find(int x){
            return f[x] == x ? x : (f[x] = find(f[x]));
        }

        void union(int x,int y){
            int fx = find(x);
            int fy = find(y);
            if(sz[fx] < sz[fy]){
                f[fx] = fy;
                sz[fy] += sz[fx];
            }else{
                f[fy] = fx;
                sz[fx] += sz[fy];
            }
        }
    }

    static boolean kruskal(){
        g.sort(Comparator.comparingInt(e ->e.w));
        UnionSet us = new UnionSet((n));
        int cnt = 0;
        int ans = 0; // 边权
        for(Edge e : g){
            if(us.find(e.u) == us.find(e.v)) continue;
            us.union(e.u,e.v);
            ans += e.w;
            if(++cnt == n-1){
                System.out.println(ans);
                return true;
            }
        }
        return false;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        n = sc.nextInt();
        m = sc.nextInt();
        for (int i = 0; i < m; i++) {
            g.add(new Edge(sc.nextInt(), sc.nextInt(),sc.nextInt()));
        }
        if(!kruskal()){
            System.out.println("impossible");
        }
    }
}