Wormholes

Wormholes

spfa 判负环

SCUACM2022集训前训练-图论 - Virtual Judge (vjudge.net)

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>
#include <queue>
using namespace std;
typedef long long ll;
const int N = 5e2 + 10;
struct Edge
{
	int to, val;
};
vector<vector<Edge> > G(N);
int n, m, q;
bool st[N];
int dist[N], cnt[N];

void init()
{
	memset(cnt, 0, sizeof cnt);
	memset(dist, 0, sizeof dist);
	memset(st, false, sizeof st);
	for (int i = 0; i < N; i++)
		G[i].clear();
}
void add(int u, int v, int w)
{
	G[u].push_back({v, w});
}

bool spfa()
{
	queue<int> q;
	for (int i = 1; i <= n; i++)
	{
		q.push(i);
		st[i] = true;
	}
	while(!q.empty())
	{
		int u = q.front();
		q.pop();
		st[u] = false;
		for (int i = 0; i < G[u].size(); i++)
		{
			int v = G[u][i].to, w = G[u][i].val;
			if (dist[v] > dist[u] + w)
			{
				dist[v] = dist[u] + w;
				cnt[v] = cnt[u] + 1;
				if (cnt[v] >= n)
					return true;
				if (!st[v])
				{
					q.push(v);
					st[v] = true;
				}
			}
		}
	}
	return false;
}
int main()
{
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	int T;
	cin >> T;
	while(T--)
	{
		cin >> n >> m >> q;
		init();
		for (int i = 1; i <= m; i++)
		{
			int u, v, w;
			cin >> u >> v >> w;
			add(u, v, w), add(v, u, w);
		}
		for (int i = 1; i <= q; i++)
		{
			int u, v, w;
			cin >> u >> v >> w;
			add(u, v, -w);
		}
		if (spfa())
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	
	return 0;
}