CCPC-EDG专场——E.Buy and Delete

acyclic:无环的

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题目链接

dijistra判最小环。

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <vector>
#include <queue>
#define INF 0x3f3f3f3f

using namespace std;

typedef pair<int,int> PII;

const int N = 2020, M = 5010;
int idx,h[N],e[M],ne[M],w[M];
int dist[N];
bool st[N];
int n,m,c;

void add(int a,int b,int c){
    
    
	e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++;
}

priority_queue<PII,vector<PII>,greater<PII> > q;
bool dijistra(int start){
    
    
	memset(dist,0x3f,sizeof dist);
	memset(st,0,sizeof st);
	
	dist[start] = 0;
//	priority_queue<PII,vector<PII>,greater<PII> > p;

	q.push({
    
    0,start});
	
	while(!q.empty()){
    
    
		auto t = q.top();
		q.pop();
		
		if(st[t.second]) 	continue;
		st[t.second] = 1;
		
		int u = t.second;
		for(int i=h[u];i!=-1;i=ne[i]){
    
    
			int j = e[i];
			
			if(j==start){
    
    
				if(dist[u] + w[i] <= c){
    
    
					return true;
				}
			}
			
			if(dist[u] + w[i] < dist[j]){
    
    
				dist[j] = dist[u] + w[i];
				q.push({
    
    dist[j],j});
			}
		}
	} 
	
	return false;
}

int main()
{
    
    
	memset(h,-1,sizeof h);
	scanf("%d%d%d",&n,&m,&c);
	
	int res = 0;
	for(int i=1;i<=m;i++){
    
    
		int a,b,w;
		scanf("%d%d%d",&a,&b,&w);
		
		add(a,b,w);
		
		if(w<=c)	res = 1;
	}
	
	if(!res)	printf("0");
	else{
    
    
		for(int i=1;i<=n;i++){
    
    
			if(dijistra(i)){
    
    
				res = 2;
				break;
			}
		}
		
		printf("%d",res);
	}
	
	
	return 0;
}