poj 3259 最短路负环

 John的农场里N块地，M条路连接两块地，W个虫洞，虫洞是一条单向路，会在你离开之前把你传送到目的地，就是当你过去的时候时间会倒退Ts。我们的任务是知道会不会在从某块地出发后又回来，看到了离开之前的自己。简化下，就是看图中有没有负权环。有的话就是可以，没有的话就是不可以了。

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;
import java.util.StringTokenizer;

public class Main {

public static void main(String[] args) {
new POJ3259().solve();
}
}

class POJ3259 {

InputReader in = new InputReader(System.in) ;
PrintWriter out = new PrintWriter(System.out) ;

final int N = 508 ;
final int M = 2500*3 ;
final int inf = Integer.MAX_VALUE ;

class Edge{
int v ;
int w ;
int next ;
Edge(int v , int w , int next) {
this.v = v ;
this.w = w ;
this.next = next ;
}
}

int n ;
int[] head = new int
;
Edge[] e = new Edge[M] ;
int eid ;
int[] dist = new int
;
boolean[] inq = new boolean
;
int[] cnt = new int
;

void add(int u , int v , int w){
e[eid] = new Edge(v , w , head[u]) ;
head[u] = eid++ ;
}

void solve(){
int t = in.nextInt() ;
while(t-- > 0){
n = in.nextInt() ;
int m = in.nextInt() ;
int w = in.nextInt() ;
eid = 0 ;
Arrays.fill(head , 1 , n+1 , -1) ;
while(m-- > 0){
int u = in.nextInt() ;
int v = in.nextInt() ;
int c = in.nextInt() ;
add(u, v, c) ;
add(v, u, c) ;
}
while(w-- > 0){
add(in.nextInt() , in.nextInt() , -in.nextInt()) ;
}
Arrays.fill(dist , 1 , 1+n , inf) ;
int res = -1 ;
for(int i = 1 ; i <= n ; i++){
if(dist[i] == inf){
if(! spfa(i)){
res = i ;
break ;
}
}
}
out.println(res == -1 ? "NO" : "YES") ;
}

out.flush() ;
}

boolean spfa(int start){
Arrays.fill(cnt, 1 , 1+n , 0) ;
Arrays.fill(inq , 1 , 1+n , false) ;
Queue<Integer> q = new LinkedList<Integer>() ;
q.add(start) ;
inq[start] = true ;
dist[start] = 0 ;
while(! q.isEmpty()){
int u = q.poll() ;
inq[u] = false ;
if(cnt[u] >= n) return false ;
for(int i = head[u] ; i != -1 ; i = e[i].next){
int v = e[i].v ;
int w = e[i].w ;
if(dist[v] > dist[u] + w){
dist[v] = dist[u] + w ;
if(! inq[v]){
inq[v] = true ;
cnt[v]++ ;
q.add(v) ;
}
}
}
}
return true ;
}
}

class InputReader {
public BufferedReader reader;
public StringTokenizer tokenizer;

public InputReader(InputStream stream) {
reader = new BufferedReader(new InputStreamReader(stream), 32768);
tokenizer = new StringTokenizer("");
}

private void eat(String s) {
tokenizer = new StringTokenizer(s);
}

public String nextLine() {
try {
return reader.readLine();
} catch (Exception e) {
return null;
}
}

public boolean hasNext() {
while (!tokenizer.hasMoreTokens()) {
String s = nextLine();
if (s == null)
return false;
eat(s);
}
return true;
}

public String next() {
hasNext();
return tokenizer.nextToken();
}

public int nextInt() {
return Integer.parseInt(next());
}

public long nextLong() {
return Long.parseLong(next());
}

public double nextDouble() {
return Double.parseDouble(next());
}

public BigInteger nextBigInteger() {
return new BigInteger(next());
}

}