POJ3259 SPFA判定负环

版权声明：个人笔记，仅供复习 https://blog.csdn.net/weixin_41162823/article/details/82114934

原题链接：POJ3259

解析：找了四五小时bug，打错俩个字母，想吃口屎冷静一下。

代码示例：

#include<iostream>
#include<cstring>
#include<queue>
#include<cstdio>
#include<vector>
using namespace std;
const int INF = 2e9;
const int maxn = 1005;
vector<int> G[maxn]; 
struct Edge{
	int from,to,dis;
};
vector<Edge> edges;
int dist[maxn];
bool vis[maxn];
int cnt[maxn];
int n;
void add_edge(int from,int to,int dis){
	edges.push_back(Edge{from,to,dis});
	int m = edges.size()-1;
	G[from].push_back(m);
}
void init(){
	for(int i = 0;i < maxn;i++)
		G[i].clear();
	for(int i = 0;i < maxn;i++)
		dist[i] = INF;
	edges.clear();
	memset(vis,false,sizeof vis);
	memset(cnt,0,sizeof cnt);
}
bool spfa(int s){
	dist[s] = 0;
	queue<int> q;
	q.push(s);
	while(!q.empty()){
		int x = q.front();
		q.pop();
		vis[x] = false;
		for(int i = 0;i < G[x].size();i++){
			Edge& e = edges[G[x][i]];
			if(dist[e.to] > dist[x] + e.dis){
				dist[e.to] = dist[x] + e.dis;
				cnt[e.to] = cnt[x] + 1; 
				if(cnt[e.to] >= n)	return false;
				if(!vis[e.to])	q.push(e.to),vis[e.to] = true;
			}
		}
	}
	return true;
}
int main()
{
	int t;
	scanf("%d",&t);
	while(t--){
		init();
		int m,w;
		scanf("%d%d%d",&n,&m,&w);
		for(int i = 0;i < m;i++){
			int u,v,val;
			scanf("%d%d%d",&u,&v,&val);
			add_edge(u,v,val);
			add_edge(v,u,val);
		}
		for(int i = 0;i < w;i++){
			int u,v,val;
			scanf("%d%d%d",&u,&v,&val);
			add_edge(u,v,-val);
		}	
		if(spfa(1))	puts("NO");
		else puts("YES");
	}
	return 0;
}