CF864F.Cities Excursions
普及/提高-
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题目描述
There are n cities in Berland. Some pairs of them are connected with m directed roads. One can use only these roads to move from one city to another. There are no roads that connect a city to itself. For each pair of cities (x,y) there is at most one road from x to y .
A path from city s to city t is a sequence of cities p1 , p2 , ... , pk , where p1=s , pk=t , and there is a road from city pi to city pi+1 for each i from 1 to k−1 . The path can pass multiple times through each city except t . It can't pass through t more than once.
A path p from s to t is ideal if it is the lexicographically minimal such path. In other words, p is ideal path from s to t if for any other path q from s to t pi<qi , where i is the minimum integer such that pi=qi .
There is a tourist agency in the country that offers q unusual excursions: the j -th excursion starts at city sj and ends in city tj .
For each pair sj , tj help the agency to study the ideal path from sj to tj . Note that it is possible that there is no ideal path from sj to tj . This is possible due to two reasons:
- there is no path from sj to tj ;
- there are paths from sj to tj , but for every such path p there is another path q from sj to tj , such that pi>qi , where i is the minimum integer for which pi=qi .
The agency would like to know for the ideal path from sj to tj the kj -th city in that path (on the way from sj to tj ).
For each triple sj , tj , kj ( 1<=j<=q ) find if there is an ideal path from sj to tj and print the kj -th city in that path, if there is any.
输入格式
The first line contains three integers n , m and q ( 2<=n<=3000 , 0<=m<=3000 , 1<=q<=4⋅105 ) — the number of cities, the number of roads and the number of excursions.
Each of the next m lines contains two integers xi and yi ( 1<=xi,yi<=n , xi=yi ), denoting that the i -th road goes from city xi to city yi . All roads are one-directional. There can't be more than one road in each direction between two cities.
Each of the next q lines contains three integers sj , tj and kj ( 1<=sj,tj<=n , sj=tj , 1<=kj<=3000 ).
输出格式
In the j -th line print the city that is the kj -th in the ideal path from sj to tj . If there is no ideal path from sj to tj , or the integer kj is greater than the length of this path, print the string '-1' (without quotes) in the j -th line.
输入输出样例
输入#1
7 7 5 1 2 2 3 1 3 3 4 4 5 5 3 4 6 1 4 2 2 6 1 1 7 3 1 3 2 1 3 5
输出#1
2 -1 -1 2 -1