# 题目

## Description

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 $N (1 \leq N \leq 500)$ fields conveniently numbered $1…N$, $M$ $(1 \leq M \leq 2500)$ paths, and $W$ $(1 \leq W \leq 200)$ 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 $F$ $(1 \leq F \leq 5)$ 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).

## Hint

For farm $1$, FJ cannot travel back in time.

For farm $2$ , FJ could travel back in time by the cycle $1\rightarrow2\rightarrow3\rightarrow1$ , arriving back at his starting location $1$ second before he leaves. He could start from anywhere on the cycle to accomplish this.

# 代码

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• 本文作者： obsidian
• 本文链接： http://ooobsidian.github.io/2017/08/07/POJ-3259/
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