P3385 【模板】负环

R53951626

Luogu/problem/P3385/P3385.cpp

@@ -0,0 +1,50 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int t, n, m, u, v, w, cnt, dist[2005];
+bool flag;
+
+struct node {
+    int u, v, w;
+
+    node() {
+        u = v = w = 0;
+    }
+    node(int _u, int _v, int _w) {
+        u = _u;
+        v = _v;
+        w = _w;
+    }
+} g[6005];
+
+int main() {
+    cin >> t;
+    while (t--) {
+        cnt = 0;
+        flag = false;
+        memset(g, 0x00, sizeof(g));
+        memset(dist, 0x3f, sizeof(dist));
+        cin >> n >> m;
+        for (int i = 1; i <= m; i++) {
+            cin >> u >> v >> w;
+            g[++cnt] = node(u, v, w);
+            if (w >= 0) g[++cnt] = node(v, u, w);
+        }
+        dist[1] = 0;
+        for (int i = 1; i <= n; i++) {
+            for (int j = 1; j <= cnt; j++) {
+                if (dist[g[j].u] == 0x3f3f3f3f) continue;
+                dist[g[j].v] = min(dist[g[j].v], dist[g[j].u] + g[j].w);
+            }
+        }
+        for (int i = 1; i <= cnt; i++) {
+            if (dist[g[i].u] == 0x3f3f3f3f || dist[g[i].v] == 0x3f3f3f3f) continue;
+            if (dist[g[i].v] > dist[g[i].u] + g[i].w) {
+                flag = true;
+            }
+        }
+        cout << (flag ? "YES" : "NO") << endl;
+    }
+    return 0;
+}