poj2377

最大生成树，注意边数组开二倍大小。注意不连通输出－1；

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

#define maxn 1005
#define maxm 20005

struct Edge
{
    int v, next, w;
    Edge(int vv, int nn, int ww) :
        v(vv), next(nn), w(ww)
    {
    }
    Edge()
    {
    }
} edge[maxm * 2];

int head[maxn], count;
bool vis[maxn];
int ans = 0;
int m, n;

bool operator< (const Edge &a, const Edge &b)
{
    return a.w < b.w;
}

void addedge(int u, int v, int w)
{
    edge[count].next = head[u];
    edge[count].v = v;
    edge[count].w = w;
    head[u] = count;
    count++;
}

void input()
{
    scanf("%d%d", &n, &m);
    for (int i = 0; i < m; i++)
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        a--, b--;
        addedge(a, b, c);
        addedge(b, a, c);
    }
}

void prim(int src)
{
    priority_queue<Edge> pq;
    int pre = 0;
    Edge temp;
    pq.push(Edge(src, 0, 0));
    while (!pq.empty())
    {
        do
        {
            temp = pq.top();
            pq.pop();
        } while (!pq.empty() && vis[temp.v]);
        if (vis[temp.v])
            return;
        vis[temp.v] = true;
        pre = temp.v;
        ans += temp.w;
        for (int i = head[pre]; i != -1; i = edge[i].next)
            if (!vis[edge[i].v])
                pq.push(edge[i]);
    }
}

int main()
{
    //freopen("t.txt", "r", stdin);
    memset(head, -1, sizeof(head));
    memset(vis, 0, sizeof(vis));
    count = 0;
    input();
    prim(0);
    bool ok = true;
    for (int i = 0; i < n; i++)
        if (!vis[i])
        {
            ok = false;
            break;
        }
    if (ok)
        printf("%d\n", ans);
    else
        printf("%d\n", -1);
    return 0;
}