Prim板子

lao_li · 2021-12-15 15:03:14 · 个人记录

适用于稠密图

#include <bits/stdc++.h>
#define rep(a, b, c) for(int a = b; a <= c; ++ a)
using namespace std;
const int MAXN = 5005, MAXM = 200005, inf = 0x3f3f3f3f;
int n, m, cnt;
int dis[MAXN], head[MAXN], vis[MAXN], now, ans; //now当前最小生成树边数 
struct EDGE {
    int v, w, nxt;
} edge[MAXM + MAXM];
priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > q; //堆优化 
void add(int u, int v, int w);
void prim();
int main() {
    ios::sync_with_stdio(false);
    cin >> n >> m;
    rep(i, 1, m) {
        int t1, t2, t3;
        cin >> t1 >> t2 >> t3;
        add(t1, t2, t3);
        add(t2, t1, t3);
    }

    prim();

    if(now == n) cout << ans << endl;
    else cout << "orz" << endl;
    //cout << now;
    return 0;
}
void add(int u, int v, int w) {
    edge[ ++ cnt].v = v;
    edge[cnt].w = w;
    edge[cnt].nxt = head[u];
    head[u] = cnt;
}
void prim() {
    memset(dis, 0x3f, sizeof(dis));
    dis[1] = 0;
    q.push(make_pair(0, 1));

    while(!q.empty() && now < n) {
        int u = q.top().second, d = q.top().first;
        q.pop();
        if(vis[u]) continue;
        ans += d;
        ++ now;
        vis[u] = 1;
        for(int i = head[u]; i; i = edge[i].nxt) {
            if(dis[edge[i].v] > edge[i].w) {
                dis[edge[i].v] = edge[i].w;
                q.push(make_pair(dis[edge[i].v], edge[i].v));
            }
        }
    }
}