2016huasacm暑假集训训练三 G - 还是畅通工程

题目链接：https://vjudge.net/contest/123674#problem/G

这题和上一道题差不多，还更简单点，直接用prim算法就行，直接贴AC代码：

 import java.io.BufferedInputStream;
 import java.util.Scanner;

 public class Main {
     final static int N = 1 << 20;
     static int n, m, a[][] = new int[105][105], b[] = new int[105], sum;

     public static void main(String[] args) {
         Scanner s = new Scanner(new BufferedInputStream(System.in));
         int u, v, w, i, j;
         while (s.hasNext()) {
             n = s.nextInt();
             if (n == 0)
                 break;

             for (i = 1; i <= n; i++)
                 for (j = 1; j <= n; j++)
                     a[i][j] = 0;
             m = n * (n - 1) / 2;
             while (m-- > 0) {
                 u = s.nextInt();
                 v = s.nextInt();
                 w = s.nextInt();
                 a[u][v] = a[v][u] = w;
             }
             sum = 0;

             prim(1);
             System.out.println(sum);
         }
         s.close();
     }

     static void prim(int u) {
         int i, j, min, v;
         for (i = 1; i <= n; i++) {
             b[i] = a[u][i];
         }
         sum = 0;
         b[u] = -1;
         for (i = 1; i <= n; i++) {
             min = N;
             v = -1;
             for (j = 1; j <= n; j++) {
                 if (b[j] != -1 && b[j] < min) {
                     v = j;
                     min = b[j];
                 }
             }
             if (v != -1) {
                 sum += b[v];
                 b[v] = -1;
                 for (j = 1; j <= n; j++) {
                     if (b[j] != -1 && a[v][j] < b[j])
                         b[j] = a[v][j];
                 }
             }
         }

     }

 }