洛谷3385 【模板】负环

一道负环模板

原题链接

负环模板，不解释。

#include<cstdio>
#include<cstring>
using namespace std;
const int N = 2010;
const int M = 3010;
int fi[N], di[M << 1], ne[M << 1], da[M << 1], dis[N], cnt[N], q[N << 10], l;
bool v[N];
inline int re()
{
	int x = 0;
	char c = getchar();
	bool p = 0;
	for (; c<'0' || c>'9'; c = getchar())
		p |= c == '-';
	for (; c >= '0'&&c <= '9'; c = getchar())
		x = x * 10 + (c - '0');
	return p ? -x : x;
}
inline void add(int x, int y, int z)
{
	di[++l] = y;
	da[l] = z;
	ne[l] = fi[x];
	fi[x] = l;
}
int main()
{
	int i, n, m, t, head, tail, x, y, z;
	bool p;
	t = re();
	while (t--)
	{
		n = re();
		m = re();
		l = 0;
		memset(fi, 0, sizeof(fi));
		memset(dis, 60, sizeof(dis));
		memset(cnt, 0, sizeof(cnt));
		memset(v, 0, sizeof(v));
		for (i = 1; i <= m; i++)
		{
			x = re();
			y = re();
			z = re();
			add(x, y, z);
			if (z >= 0)
				add(y, x, z);
		}
		head = 0;
		tail = p = 1;
		dis[1] = 0;
		q[1] = 1;
		while (head != tail && p)
		{
			x = q[++head];
			v[x] = 0;
			for (i = fi[x]; i; i = ne[i])
			{
				y = di[i];
				if (dis[y] > dis[x] + da[i])
				{
					dis[y] = dis[x] + da[i];
					cnt[y] = cnt[x] + 1;
					if (cnt[y] >= n)
					{
						p = 0;
						break;
					}
					if (!v[y])
					{
						q[++tail] = y;
						v[y] = 1;
					}
				}
			}
		}
		if (p)
			printf("N0\n");
		else
			printf("YE5\n");
	}
	return 0;
}