HDU1863 – 畅通工程

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最小生成树模板

  • Kruskal – 基于并查集
  • Prim – 基于贪心

Kruskal

C++
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#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long LL;
 
const LL maxn = 100 + 1;
LL father[maxn];
LL n, m;
 
struct edge {
    LL from, to, cost;
 
    edge(LL from_ = 0, LL to_ = 0, LL cost_ = 0):
        from(from_), to(to_), cost(cost_) {}
 
    friend inline bool operator < (const edge &e_1, const edge &e_2) {
        return e_1.cost < e_2.cost;
    }
} E[maxn * maxn];
 
void init() {
    for (LL i = 1; i <= n; ++i)
        father[i] = i;
}
 
LL find(LL u) {
    return father[u] == u ? father[u] : father[u] = find(father[u]);
}
 
void join(LL u, LL v) {
    father[find(v)] = find(u);
}
 
LL Kruskal() {
    sort(E + 1, E + m + 1);
    init();
    LL ret = 0;
    for (LL i = 1; i <= m; ++i) {
        if (find(E[i].from) != find(E[i].to)) {
            ret += E[i].cost;
            join(E[i].from, E[i].to);
        }
    }
    return ret;
}
 
int main() {
 
    ios::sync_with_stdio(false);
 
    LL ans, is_connect;
    while (cin >> m >> n && m != 0) {
        for (LL i = 1; i <= m; ++i)
            cin >> E[i].from >> E[i].to >> E[i].cost;
        ans = Kruskal();
 
        is_connect = true;
        for (LL i = 1; i <= n; ++i) {
            if (find(1) != find(i))
                is_connect = false;
        }
 
        if (!is_connect) cout << "?" << endl;
        else cout << ans << endl;
    }
 
    return 0;
}

Prim

C++
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#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long LL;
 
const LL maxn = 100 + 1;
 
struct edge {
    LL to, cost;
 
    edge(LL to_ = 0, LL cost_ = 0):
        to(to_), cost(cost_) {}
 
    friend bool operator > (const edge &e_1, const edge &e_2) {
        return e_1.cost > e_2.cost;
    }
};
 
LL n, m;
vector <edge> g[maxn];
priority_queue <edge, vector<edge>, greater<edge> > q;
bool vis[maxn];
 
LL Prim() {
    memset(vis, 0, sizeof vis);
    LL ret = 0;
    vis[1] = 1;
    for (unsigned i = 0; i < g[1].size(); ++i) {
        q.push(g[1][i]);
    }
 
    edge e;
 
    while (!q.empty()) {
        e = q.top();
        q.pop();
        if (!vis[e.to]) {
            vis[e.to] = 1;
            ret += e.cost;
            for (unsigned i = 0; i < g[e.to].size(); ++i) {
                q.push(g[e.to][i]);
            }
        }
    }
 
    return ret;
}
 
int main() {
    ios::sync_with_stdio(false);
 
    LL tu, tv, tc, ans;
 
    while (cin >> m >> n && m != 0) {
        for (LL i = 1; i <= n; ++i)
            g[i].clear();
 
        while (!q.empty()) {
            q.pop();
        }
 
        for (LL i = 1; i <= m; ++i) {
            cin >> tu >> tv >> tc;
            g[tu].push_back(edge(tv, tc));
            g[tv].push_back(edge(tu, tc));
        }
 
        ans = Prim();
 
        for (LL i = 1; i <= n; ++i) {
            if (!vis[i]) {
                ans = -1;
            }
        }
 
        if (ans == -1) cout << "?" << endl;
        else cout << ans << endl;
    }
 
    return 0;
}

 

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