IOI2006 D0-3:HIGHWAYS
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IOI2006 D0-3
Highways Country: Official Version
IOI’06 English
Practice – Task 3 Version 1.0
HIGHWAYS
There are c cities in the Yucatan Peninsula. These cities are interconnected via h highways.
Because of its flat surface, the highways of the peninsula have very few curves and drivers tend to
over speed. The government wants to implement a new traffic system that will set radars to
measure the speed of cars in the highways.
The government can afford to put radars in at most c highways. The governor wants to set the
radars so that for every city in the peninsula there is an odd number of highways that leave from
that city that have the radar system.
Help the governor achieve his goal.
The figure shows a map of the cities and the highways.
Circles represent the cities and lines represent the highways.
Thick lines represent the highways which have the radar
system. You can see that for every city there is an odd
number of highways that have the system. Also the number
of highways with the radar system is less than c.
The cities will be arbitrarily numbered from 1 to c.
TASK
Write a program that given the map of the cities and the highways decides on which highways to
set the radar system so that the goal of the governor is achieved and the budget is not exceeded.
CONSTRAINTS
0 < c _ 10 000
0 < h _ 100 000
INPUT
Your program must read from the file highways.in the following data
highways.in DESCRIPTION
6 7
1 2
2 4
4 6
3 5
4 5
2 3
5 6
LINE 1: Contains 2 space-separated integers that represent c and h
respectively
NEXT h LINES: Each line contains 2 space-separated integers that
represent a highway. The integers represent the cities in each
end of the highway.
OUTPUT
Your program must write to the file highways.out the following data
highway.out DESCRIPTION
4
1 2
2 3
2 4
5 6
LINE 1: Must contain one integer that represents the number of
highways in which the radar system will be implemented or –1
if it is impossible to achieve the desired goal.
NEXT LINES: Must contain 2 space-separated integers that represent
the highway in which the system will be implemented.
GRADING INFO
In one test case every test run will satisfy the following constraints:
0 < c _ 50
0 < h _ 1 000
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