Prim's algorithm for minimum spanning tree - merging of vertices

import java.util.ArrayList;
import java.util.Scanner;
/*
样例输入
4 4
1 2 1
2 3 4
2 4 2
3 4 3
样例输出
6

样例输入
6 9
1 2 1
2 4 11
4 6 3
6 5 4
5 3 13
3 1 2
2 3 6
3 4 9
4 5 7
样例输出
19
*/
public class Main{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();//顶点数
        int m=sc.nextInt();//边数
        int [][]c=new int[n+1][n+1];

        for (int i = 0; i < m; i++) {
            int v1=sc.nextInt();
            int v2=sc.nextInt();
            int cost=sc.nextInt();
            c[v1][v2]=c[v2][v1]=cost;
        }

        ArrayList<Integer> S=new ArrayList<Integer>();
        ArrayList<Integer> V=new ArrayList<Integer>();
        ArrayList<Integer> C=new ArrayList<Integer>();

        S.add(1);
        for (int i =2; i <=n; i++) {
            V.add(i);
        }

        while(S.size()<n){
            Integer j=0;
            int lowCost=Integer.MAX_VALUE;
            for (Integer v1 : S) {
                for (Integer v2 : V) {
                    if(c[v1][v2]!=0 && c[v1][v2]<lowCost){
                        lowCost=c[v1][v2];
                        j=v2;
                    }
                }
            }
            S.add(j);
            V.remove(j);
            C.add(lowCost);
        }


        int sum=0;
        for (Integer cost : C) {
            sum+=cost;
        }
        System.out.println(sum);
    }
}