47 lines
1.3 KiB
C++
47 lines
1.3 KiB
C++
// FIFO SPFA；输入必须没有源点可达的负环，最坏时间 O(nm)。
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// 输入输出同 P3371；一般负权图应使用第 4 份中的判环版本。
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#include <iostream>
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#include <vector>
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#include <queue>
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using namespace std;
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using ll = long long;
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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);
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cin.tie(nullptr);
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int n, m, s;
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if (!(cin >> n >> m >> s)) return 0;
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vector<vector<Edge>> g(n + 1);
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for (int i = 0; i < m; ++i) {
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int u, v; ll w;
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cin >> u >> v >> w;
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g[u].push_back({v, w});
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}
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const ll INF = (1LL << 60);
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vector<ll> dis(n + 1, INF);
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vector<char> in_queue(n + 1, false);
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queue<int> q;
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dis[s] = 0;
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q.push(s);
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in_queue[s] = true;
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while (!q.empty()) {
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int u = q.front();
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q.pop();
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in_queue[u] = false; // 离队后仍允许再次排队
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for (const auto &e : g[u]) {
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int v = e.to;
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ll nd = dis[u] + e.w;
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if (nd < dis[v]) {
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dis[v] = nd; // 已在队列中也必须更新距离
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if (!in_queue[v]) {
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q.push(v);
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in_queue[v] = true;
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}
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}
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}
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}
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for (int i = 1; i <= n; ++i)
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cout << (dis[i] == INF ? 2147483647LL : dis[i])
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<< (i == n ? '\n' : ' ');
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}
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