2011 Canadian Computing Competition, Stage 2

Day 1, Problem 2: Vampire Tunnels

You are a vampire, and you want to travel from some point A to another point B. You may travel in the sunshine above ground or avoid the sunshine by travelling underground via certain tunnels. You have mapped out the area you wish to travel, and have found some secret tunnels between some points, some other points that you can walk between above ground. Both the tunnels and above ground paths are bidirectional. Given that you can't be exposed to the sunlight for more than S seconds in total, you want to minimize the total travel time (given that you have a constant speed of 1 unit of distance per second).

Input Format

On the first line of input, you have the number S (0 ≤ S ≤ 3600), the maximum number of seconds that you can be exposed to the sun. On the next line is the number N (2 ≤ N ≤ 1600), which is the number of points, and the number E (1 ≤ E ≤ 10000), which is the number of connections between these N points, separated by one space.

The next E lines each contain information about the connections between points. Specifically, each of these lines contains four integers: s (0 ≤ s ≤ N-1), one end point of a connection; t (0 ≤ t ≤ N-1, s ≠ t), the other end point of a connection; d (1 ≤ d ≤ 10000), the distance between s and t; and u, which is 1 if this connection is above ground and 0 if it is underground.

Note: for 30% of the marks for this question, you can assume N ≤ 50.

Output Format

The output is one integer, which is the minimum amount of time required to get from point 0 to point N-1, with the constraint that there are not more than S seconds of exposure to the sun. If there is no possible path which satisfies the constraint, output -1.

Sample Input

3
4 6
0 1 3 1
0 2 4 1
0 3 10 1
1 2 3 0
1 3 1 1
2 3 3 0

Sample Output

9

Explanation

The path 0 → 1 → 2 → 3 gives a total travel time of 9 seconds with 3 seconds of exposure to the sun. All other paths either required more time (e.g., 0 → 3 uses 10 seconds) or overexposure to the sun (e.g., 0 → 1 → 3 exposes to the sun for 4 seconds).

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Best Solutions

Point Value: 15 (partial)
Time Limit: 2.00s
Memory Limit: 256M
Added: Jun 05, 2011

Languages Allowed:
C++03, PAS, C, HASK, ASM, RUBY, PYTH2, JAVA, PHP, SCM, CAML, PERL, C#, C++11, PYTH3

Comments (Search)

The idea for this problem arose during a few discussions in our suite at Waterloo. It was originally motivated by the joke that CS students spend all their time inside (as a matter of fact, my eyes used to hurt every time I went out into the bright sunlight).

The data I posted is directly from the CEMC website. You might consider emailing Troy and asking whether there could have been some sort of mistake. I will also code solutions when I have the time.

I fixed the problem. It was my fault. Sorry about that.