Initial commit: C++ courseware

2.Course/2.深入浅出程序设计竞赛（提高篇）/最短路/C++源码/07_05_p1993.cpp

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+// P1993 小K的农场。上界边 x[v] <= x[u]+w，全图判负环。
+#include <bits/stdc++.h>
+using namespace std;
+using ll = long long;
+int main() {
+    ios::sync_with_stdio(false); cin.tie(nullptr);
+    int n, m; if (!(cin >> n >> m)) return 0;
+    vector<vector<pair<int,ll>>> g(n + 1);
+    auto add = [&](int u, int v, ll w) { g[u].push_back({v,w}); };
+    for (int i = 0, type, a, b; i < m; ++i) {
+        cin >> type >> a >> b; ll c;
+        if (type == 1) { cin >> c; add(a,b,-c); }
+        else if (type == 2) { cin >> c; add(b,a,c); }
+        else { add(a,b,0); add(b,a,0); }
+    }
+    vector<ll> dist(n + 1, 0);
+    vector<int> len(n + 1, 0);
+    vector<bool> inq(n + 1, true);
+    queue<int> q; for (int i = 1; i <= n; ++i) q.push(i);
+    while (!q.empty()) {
+        int u = q.front(); q.pop(); inq[u] = false;
+        for (auto [v,w] : g[u]) if (dist[v] > dist[u] + w) {
+            dist[v] = dist[u] + w; len[v] = len[u] + 1;
+            if (len[v] >= n) { cout << "No\n"; return 0; }
+            if (!inq[v]) { q.push(v); inq[v] = true; }
+        }
+    }
+    cout << "Yes\n";
+}