POJ 2395 Out of Hay

http://poj.org/problem?id=2395

裸最小生成树 输出树中最大cost的边值

直接prim

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <queue>
#include <algorithm>
#define READ() freopen("in.txt", "r", stdin);
#define MAXV 2007
#define MAXE 20007
#define INF 0x3f3f3f3f3f3f3f3f

using namespace std;
int N, M;
typedef long long ll;
typedef pair<ll, int> P;

struct Edge
{
    int to, next;
    ll cost;
    Edge() {}
    Edge(int to, ll cost, int next) : to(to), cost(cost), next(next) {}
}edge[MAXE];

int head[MAXV];
int num = 0;
void Add(int from, int to, ll cost)
{
    edge[num] = Edge(to, cost, head[from]);
    head[from] = num++;
}

int prim()
{
    ll dist[MAXV];
    ll rec[MAXV], r = 0;
    bool use[MAXV];
    priority_queue<P, vector<P>, greater<P> > que; // 从小到大排啊
    fill(dist, dist+MAXV, INF);
    fill(use, use+MAXV, false);
    dist[1] = 0;
    que.push(P(dist[1], 1));
    while (!que.empty())
    {
        P p = que.top();
        que.pop();
        ll d = p.first;
        int v = p.second;
        if (!use[v]) rec[r++] = dist[v];
        use[v] = true;
        if (dist[v] < d) continue;
        int t = head[v];
        while (t != -1)
        {
            Edge e = edge[t];
            if (!use[e.to] && dist[e.to] > e.cost)
            {
                dist[e.to] = e.cost;
                que.push(P(dist[e.to], e.to));
            }
            t = e.next;
        }
    }
    sort(rec, rec+r);
    return rec[r-1];
}



int main()
{
    READ()
    scanf("%d%d", &N, &M);
    memset(edge, -1, sizeof(edge));
    memset(head, -1, sizeof(head));
    for (int i = 0; i < M; i++)
    {
        int from, to;
        ll cost;
        scanf("%d%d", &from, &to);
        scanf("%lld", &cost);
        Add(from, to, cost);
        Add(to, from, cost);
    }
    ll ans = prim();
    cout << ans << endl;
}