47 lines
1.4 KiB
C++
47 lines
1.4 KiB
C++
// P1629 / 教材例 10-3：有向正权图，题目保证任意两点互相可达。
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// 输入 n m，随后 m 行 u v w；顶点从 1 编号。
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#include <iostream>
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#include <vector>
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#include <queue>
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#include <utility>
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#include <functional>
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using namespace std;
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using ll = long long;
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using State = pair<ll, int>;
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struct Edge { int to; ll w; };
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vector<ll> dijkstra(const vector<vector<Edge>> &g, int s) {
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const ll INF = (1LL << 60);
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vector<ll> dis(g.size(), INF);
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priority_queue<State, vector<State>, greater<State>> q;
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dis[s] = 0; q.push({0, s});
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while (!q.empty()) {
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State cur = q.top(); q.pop();
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ll d = cur.first; int u = cur.second;
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if (d != dis[u]) continue;
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for (const auto &e : g[u]) {
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ll nd = d + e.w;
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if (nd < dis[e.to]) {
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dis[e.to] = nd;
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q.push({nd, e.to});
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}
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}
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}
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return dis;
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}
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int main() {
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ios::sync_with_stdio(false); cin.tie(nullptr);
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int n, m;
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if (!(cin >> n >> m)) return 0;
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vector<vector<Edge>> g(n + 1), rg(n + 1);
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for (int i = 0; i < m; ++i) {
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int u, v; ll w; cin >> u >> v >> w;
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g[u].push_back({v, w});
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rg[v].push_back({u, w});
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}
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vector<ll> out = dijkstra(g, 1);
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vector<ll> back = dijkstra(rg, 1);
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ll ans = 0;
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for (int i = 2; i <= n; ++i) ans += out[i] + back[i];
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cout << ans << '\n';
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}
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