dfs_SPFA 判负环

感觉有点像tarjan求SCC

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <cmath>
using namespace std;
const int MAXN=400005;
int init(){
	int rv=0,fh=1;
	char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-') fh=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9'){
		rv=(rv<<1)+(rv<<3)+c-'0';
		c=getchar();
	}
	return fh*rv;
}
struct edge{
	int to,nxt,dis;
}e[MAXN];
int nume,n,m,head[MAXN],T,dis[MAXN];
bool f[MAXN];
void adde(int from,int to,int dis){
	e[++nume].to=to;
	e[nume].dis=dis;
	e[nume].nxt=head[from];
	head[from]=nume;
}
bool dfs_SPFA(int u){
	f[u]=1;
	for(int i=head[u];i;i=e[i].nxt){
		int v=e[i].to;
		if(dis[v]>dis[u]+e[i].dis){
			
			if(f[v]) return 1;
			dis[v]=dis[u]+e[i].dis;
			if(dfs_SPFA(v)) return 1;
		}
	}
	f[u]=0;
	return 0;
}
int main(){
	freopen("in.txt","r",stdin);
	T=init();
	while(T--){
		bool isis=0;
		memset(head,0,sizeof(head));
		memset(f,0,sizeof(f));
		memset(dis,0,sizeof(dis));
		nume=0;
		n=init();m=init();
		for(int i=1;i<=m;i++){
			int u=init(),v=init(),di=init();
			adde(u,v,di);
			if(di>=0) adde(v,u,di);
		}
		for(int i=1;i<=n;i++){
			if(dfs_SPFA(i)){printf("YE5
");isis=1;break;}
		}
		if(!isis) printf("N0
");
	}
	
	fclose(stdin);
	return 0;
}