poj1287

最小生成树

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxn 55
#define inf 0x3f3f3f3f

int n, m;
int vis[maxn];
int lowc[maxn];
int cost[maxn][maxn];

int prim()
{
    int i, j, p;
    int minc, res = 0;
    memset(vis, 0, sizeof(vis));
    vis[0] = 1;
    for (i = 1; i < n; i++)
        lowc[i] = cost[0][i];
    for (i = 1; i < n; i++)
    {
        minc = inf;
        p = -1;
        for (j = 0; j < n; j++)
            if ((0 == vis[j] && minc > lowc[j]))
            {
                minc = lowc[j];
                p = j;
            }
        if (inf == minc)
            return -1;
        res += minc;
        vis[p] = 1;
        for (j = 0; j < n; j++)
            if (0 == vis[j] && lowc[j] > cost[p][j])
                lowc[j] = cost[p][j];
    }
    return res;
}

void input()
{
    scanf("%d", &m);
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            cost[i][j] = inf;
    for (int i = 0; i < m; i++)
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        a--;
        b--;
        if (cost[a][b] > c)
            cost[a][b] = cost[b][a] = c;
    }
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%d", &n), n)
    {
        input();
        printf("%d\n", prim());
    }

    return 0;
}