【模板】prim的heap优化

简单的代码。。

时间复杂度为O((n + m)logn)

大部分情况下还是跑不过kruskal的，慎用。

#include <cstdio>
#include <queue>
#include <cstring>
#define heap pair<int, int>

using namespace std;

int n, m, cnt, ans;
int head[5001], to[400001], next[400001], val[400001];
bool vis[5001];
priority_queue <heap, vector <heap>, greater <heap> > q;

inline void add(int x, int y, int z)
{
    to[cnt] = y;
    val[cnt] = z;
    next[cnt] = head[x];
    head[x] = cnt++;
}

inline void queue_prim()
{
    int i, u, v, tot = n;
    heap x;
    q.push(make_pair(0, 1));
    while(!q.empty() && tot)
    {
        x = q.top();
        q.pop();
        u = x.second;
        if(vis[u]) continue;
        vis[u] = 1;
        ans += x.first;
        tot--;
        for(i = head[u]; i != -1; i = next[i])
        {
            v = to[i];
            if(!vis[v]) q.push(make_pair(val[i], v));
        }
    }
}

int main()
{
    int i, x, y, z;
    memset(head, -1, sizeof(head));
    scanf("%d %d", &n, &m);
    for(i = 1; i <= m; i++)
    {
        scanf("%d %d %d", &x, &y, &z);
        add(x, y, z);
        add(y, x, z);
    }
    queue_prim();
    printf("%d", ans);
    return 0;
}