0
1
mirror of https://git.sb/baoshuo/OI-codes.git synced 2024-11-08 15:18:46 +00:00

P3385 【模板】负环

https://www.luogu.com.cn/record/92000229
This commit is contained in:
Baoshuo Ren 2022-10-29 10:44:48 +08:00
parent 7bdcaf5f2c
commit 28b2dc42c4
Signed by: baoshuo
GPG Key ID: 00CB9680AB29F51A

View File

@ -1,51 +1,79 @@
#include <bits/stdc++.h>
#include <iostream>
#include <algorithm>
#include <queue>
#include <utility>
#include <vector>
using namespace std;
using std::cin;
using std::cout;
const char endl = '\n';
int t, n, m, u, v, w, cnt, dist[2005];
bool flag;
const int N = 2e3 + 5;
const int INF = 0X3f3f3f3f;
struct node {
int u, v, w;
int t, n, m, dist[N], cnt[N];
std::vector<std::pair<int, int>> g[N];
bool vis[N];
node() {
u = v = w = 0;
bool spfa() {
std::fill_n(cnt, N, 0);
std::fill_n(vis, N, false);
std::fill_n(dist, N, INF);
std::queue<int> q;
q.emplace(1);
dist[1] = 0;
vis[1] = true;
while (!q.empty()) {
int u = q.front();
q.pop();
vis[u] = false;
for (auto e : g[u]) {
int v = e.first,
w = e.second;
if (dist[v] > dist[u] + w) {
dist[v] = dist[u] + w;
if (!vis[v]) {
cnt[v] = cnt[u] + 1;
if (cnt[v] >= n) return false;
vis[v] = true;
q.emplace(v);
}
}
}
}
node(int _u, int _v, int _w) {
u = _u;
v = _v;
w = _w;
}
} g[6005];
return true;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
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++) {
for (int i = 1, u, v, w; i <= m; i++) {
cin >> u >> v >> w;
g[++cnt] = node(u, v, w);
if (w >= 0) g[++cnt] = node(v, u, w);
g[u].emplace_back(v, w);
if (w >= 0) g[v].emplace_back(u, w);
}
dist[1] = 0;
cout << (!spfa() ? "YES" : "NO") << endl;
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);
g[i].clear();
}
}
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;
}