51 lines
1.6 KiB
C++
51 lines
1.6 KiB
C++
// P4568 / 教材例 10-2：隐式分层图，最多 k 次免费。
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// n m k；s t；m 行 u v w。城市从 0 编号，无向非负边。
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// 课堂扩展约定：如果没有路线，输出 -1；原题未指定此情况的输出。
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#include <iostream>
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#include <vector>
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#include <queue>
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#include <tuple>
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#include <functional>
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#include <algorithm>
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using namespace std;
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using ll = long long;
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using State = tuple<ll, int, int>;
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struct Edge { int to; ll w; };
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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, k, s, t;
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if (!(cin >> n >> m >> k >> s >> t)) return 0;
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vector<vector<Edge>> g(n);
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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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g[v].push_back({u, w});
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}
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const ll INF = (1LL << 60);
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vector<vector<ll>> dis(k + 1, vector<ll>(n, INF));
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priority_queue<State, vector<State>, greater<State>> q;
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dis[0][s] = 0;
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q.push({0, s, 0});
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while (!q.empty()) {
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State cur = q.top(); q.pop();
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ll d = get<0>(cur);
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int u = get<1>(cur), j = get<2>(cur);
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if (d != dis[j][u]) continue;
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for (const auto &e : g[u]) {
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int v = e.to;
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ll nd = d + e.w;
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if (nd < dis[j][v]) {
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dis[j][v] = nd;
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q.push({nd, v, j});
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}
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if (j < k && d < dis[j + 1][v]) {
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dis[j + 1][v] = d;
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q.push({d, v, j + 1});
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}
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}
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}
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ll ans = INF;
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for (int j = 0; j <= k; ++j) ans = min(ans, dis[j][t]);
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cout << (ans == INF ? -1 : ans) << '\n';
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}
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