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OI-codes/Luogu/P3385/P3385.cpp

51 lines
1.2 KiB
C++

#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;
}