poj 3259 Wormholes 判断负权回路

       这题没啥好说的，题目看了很久，才明白，原来是虫洞。用判断是否存在负权环，用bellman_ford即可

 

#include<iostream>
using namespace std;

const int MAX = 6000;
const int INF = 1000000000;

struct edge
{
	int u,v;
	int cost;
};

edge e[MAX];

int arcs[505][505];
int n,m,w;
int d[MAX];
int count;

bool bellman_ford()
{
	int u,v,w;
	bool isfinish;
	for (int i = 0; i <= n; i++)
		d[i] = INF;

	d[1] = 0;
	for (int i = 1; i <= n; i++)
	{
		isfinish = true;
		for (int j = 0; j < count; j++)
		{
			u = e[j].u;
			v = e[j].v;
			w = e[j].cost;
			if (d[v] > d[u] + w)
			{
				d[v] = d[u] + w;
				isfinish = false;
			}
		}

		if (isfinish)  break;
	}

	for (int j = 0; j < count; j++)
	{
		u = e[j].u;
		v = e[j].v;
		w = e[j].cost;
		if (d[v] > d[u] + w)
			return false;
	}

	return true;
};

int main()
{
	int cases;
	int a, b, c;

	cin >> cases;

	while (cases--)
	{
		scanf("%d%d%d", &n, &m, &w);

		for (int i = 1; i <= n; i++)
			for (int j = 1; j <= n; j++)
				arcs[i][j] = INF;

		for (int i = 0; i < m; i++)
		{
			scanf("%d%d%d", &a, &b, &c);
			arcs[a][b] = min(arcs[a][b], c);
			arcs[b][a] = arcs[a][b];
		}

		for (int i = 0; i < w; i++)
		{
			scanf("%d%d%d", &a, &b, &c);
			c = -c;
			arcs[a][b] = min(arcs[a][b], c);
		}

		count = 0;
		for (int i = 1; i <= n; i++)
			for (int j = 1; j <= n; j++)
				if (arcs[i][j] < INF)
				{
					e[count].u = i;
					e[count].v = j;
					e[count++].cost = arcs[i][j];
				}

		if (bellman_ford())
			cout << "NO" << endl;
		else
			cout << "YES" << endl;
	}
	return 0;
}