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https://git.sb/baoshuo/OI-codes.git
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80 lines
1.4 KiB
C++
80 lines
1.4 KiB
C++
#include <iostream>
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#include <algorithm>
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#include <queue>
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#include <utility>
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#include <vector>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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const int N = 2e3 + 5;
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const int INF = 0X3f3f3f3f;
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int t, n, m, dist[N], cnt[N];
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std::vector<std::pair<int, int>> g[N];
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bool vis[N];
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bool spfa() {
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std::fill_n(cnt, N, 0);
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std::fill_n(vis, N, false);
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std::fill_n(dist, N, INF);
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std::queue<int> q;
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q.emplace(1);
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dist[1] = 0;
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vis[1] = 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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vis[u] = false;
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for (auto e : g[u]) {
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int v = e.first,
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w = e.second;
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if (dist[v] > dist[u] + w) {
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dist[v] = dist[u] + w;
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if (!vis[v]) {
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cnt[v] = cnt[u] + 1;
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if (cnt[v] >= n) return false;
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vis[v] = true;
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q.emplace(v);
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}
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}
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}
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}
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return true;
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}
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> t;
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while (t--) {
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cin >> n >> m;
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for (int i = 1, u, v, w; i <= m; i++) {
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cin >> u >> v >> w;
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g[u].emplace_back(v, w);
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if (w >= 0) g[v].emplace_back(u, w);
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}
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cout << (!spfa() ? "YES" : "NO") << endl;
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for (int i = 1; i <= n; i++) {
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g[i].clear();
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}
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}
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return 0;
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}
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