Destroying
the bus stations
Time
Limit: 4000/2000 MS (Java/Others) Memory Limit:
32768/32768 K (Java/Others) Total Submission(s):
2072 Accepted Submission(s): 647
Problem Description
Gabiluso is one of the greatest spies in his country. Now
he’s trying to complete an “impossible” mission ----- to make it slow for the
army of City Colugu to reach the airport. City Colugu has n bus stations and m
roads. Each road connects two bus stations directly, and all roads are one way
streets. In order to keep the air clean, the government bans all military
vehicles. So the army must take buses to go to the airport. There may be more
than one road between two bus stations. If a bus station is destroyed, all roads
connecting that station will become no use. What’s Gabiluso needs to do is
destroying some bus stations to make the army can’t get to the airport in k
minutes. It takes exactly one minute for a bus to pass any road. All bus
stations are numbered from 1 to n. The No.1 bus station is in the barrack and
the No. n station is in the airport. The army always set out from the No. 1
station. No.1 station and No. n station can’t be destroyed because of the heavy
guard. Of course there is no road from No.1 station to No. n station.
Please
help Gabiluso to calculate the minimum number of bus stations he must destroy to
complete his mission.
Input
There are several test cases. Input ends with three
zeros.
For each test case:
The first line contains 3 integers, n, m and k.
(0< n <=50, 0< m<=4000, 0 < k < 1000) Then m lines follows.
Each line contains 2 integers, s and f, indicating that there is a road from
station No. s to station No. f.
Output
For each test case, output the minimum number of stations
Gabiluso must destroy.
Sample Input
5 7 3
1 3
3 4
4 5
1 2
2 5
1 4
4 5
0 0 0
Sample Output
2
Source
题意：
Gabiluso是
HDUOJ----2485 Destroying the bus stations