问题描述：
英语翻译
While exploring his many farms,Farmer John has discovered a number of amazing wormholes.A wormhole is very peculiar because it is a one-way path that delivers you to its destination at a time that is BEFORE you entered the wormhole!Each of FJ's farms comprises N (1 ≤ N ≤ 500) fields conveniently numbered 1..N,M (1 ≤ M ≤ 2500) paths,and W (1 ≤ W ≤ 200) wormholes.
As FJ is an avid time-traveling fan,he wants to do the following:start at some field,travel through some paths and wormholes,and return to the starting field a time before his initial departure.Perhaps he will be able to meet himself :) .
To help FJ find out whether this is possible or not,he will supply you with complete maps to F (1 ≤ F ≤ 5) of his farms.No paths will take longer than 10,000 seconds to travel and no wormhole can bring FJ back in time by more than 10,000 seconds.
Input
Line 1:A single integer,F.F farm descriptions follow.
Line 1 of each farm:Three space-separated integers respectively:N,M,and W
Lines 2..M+1 of each farm:Three space-separated numbers (S,E,T) that describe,respectively:a bidirectional path between S and E that requires T seconds to traverse.Two fields might be connected by more than one path.
Lines M+2..M+W+1 of each farm:Three space-separated numbers (S,E,T) that describe,respectively:A one way path from S to E that also moves the traveler back T seconds.
Output
Lines 1..F:For each farm,output "YES" if FJ can achieve his goal,otherwise output "NO" (do not include the quotes).
Sample Input
2
3 3 1
1 2 2
1 3 4
2 3 1
3 1 3
3 2 1
1 2 3
2 3 4
3 1 8
Sample Output
NO
YES
While exploring his many farms,Farmer John has discovered a number of amazing wormholes.A wormhole is very peculiar because it is a one-way path that delivers you to its destination at a time that is BEFORE you entered the wormhole!Each of FJ's farms comprises N (1 ≤ N ≤ 500) fields conveniently numbered 1..N,M (1 ≤ M ≤ 2500) paths,and W (1 ≤ W ≤ 200) wormholes.
As FJ is an avid time-traveling fan,he wants to do the following:start at some field,travel through some paths and wormholes,and return to the starting field a time before his initial departure.Perhaps he will be able to meet himself :) .
To help FJ find out whether this is possible or not,he will supply you with complete maps to F (1 ≤ F ≤ 5) of his farms.No paths will take longer than 10,000 seconds to travel and no wormhole can bring FJ back in time by more than 10,000 seconds.
Input
Line 1:A single integer,F.F farm descriptions follow.
Line 1 of each farm:Three space-separated integers respectively:N,M,and W
Lines 2..M+1 of each farm:Three space-separated numbers (S,E,T) that describe,respectively:a bidirectional path between S and E that requires T seconds to traverse.Two fields might be connected by more than one path.
Lines M+2..M+W+1 of each farm:Three space-separated numbers (S,E,T) that describe,respectively:A one way path from S to E that also moves the traveler back T seconds.
Output
Lines 1..F:For each farm,output "YES" if FJ can achieve his goal,otherwise output "NO" (do not include the quotes).
Sample Input
2
3 3 1
1 2 2
1 3 4
2 3 1
3 1 3
3 2 1
1 2 3
2 3 4
3 1 8
Sample Output
NO
YES
问题解答：
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