852. spfa判断负环

https://www.acwing.com/problem/content/submission/code_detail/7062672/

AcWing/852/852.cpp

@@ -0,0 +1,37 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, m, u, v, w, dist[100005], cnt[100005];
+vector<pair<int, int>> g[100005];
+
+bool spfa() {
+    memset(dist, 0x3f, sizeof(dist));
+    queue<int> q;
+    for (int i = 1; i <= n; i++) {
+        q.push(i);
+    }
+    while (!q.empty()) {
+        int t = q.front();
+        q.pop();
+        for (auto i : g[t]) {
+            if (dist[i.first] > dist[t] + i.second) {
+                dist[i.first] = dist[t] + i.second;
+                cnt[i.first] = cnt[t] + 1;
+                if (cnt[i.first] >= n) return true;
+                q.push(i.first);
+            }
+        }
+    }
+    return false;
+}
+
+int main() {
+    cin >> n >> m;
+    for (int i = 0; i < m; i++) {
+        cin >> u >> v >> w;
+        g[u].push_back(make_pair(v, w));
+    }
+    cout << (spfa() ? "Yes" : "No") << endl;
+    return 0;
+}