1. Problem Solving on ACM
International Collegiate
Programming Contest
Fedor Tsarev, ACM ICPC World
Champion 2008
St. Petersburg University of IT,
Mechanics & Optics
18.10.2010
ETH Zurich

2. 2
Epigraph
The whole is more than
the sum of its parts
(Aristotle)

3. 3
Perfect Team
 Common code-style
(indents, variable naming,
…)
 Common patterns of
algorithm implementation
 Everyone should know
strong and weak points of
other members of the
team

4. 4
Start of the Contest
 Write a template
 Read problem statements:
 Starting with the first
problem
 Starting with the last
problem
 Do not try to solve the first
problem you have read –
find the simplest problem
 Every member must know
his role at the start of the
contest

5. 5
Problems Status
№ Member 1 Member 2 Member 3 Comments
A
+ Graph theory
B
+
C
+
D
+
…

6. 6
One hour from the start of the
contest…
№ Member 1 Member 2 Member 3 Comments
A
+ Graph theory
B
+ + + KMP
C
+ + + DP over subsets
D
+ + + Geometry
…
+ + +

7. 7
How to solve a problem
1. Read the statement carefully
2. Invent an algorithm
3. Discuss the algorithm with another member
of your team
4. Discuss the implementation with another
member of your team
5. Write a program
6. Test your solution

8. 8
Submitting a Solution
 Save the source file before submitting
 Compile it
 Always test the solution on example tests and
on all tests you have:
 Corner cases
 Maximal tests (checking time limit and memory
limit)
 Print the source code after submitting (on the
official contest)

9. 9
If your solution is not
accepted…
 … then you have a bug in the program 
 To find it carefully read the printout
 Never read the code from the screen
 If you find a bug do not fix it right now on the
computer – there are more bugs in the program
 Fix the bug in the printout
 Try to explain your code to another member of
your team
 Write a slower solution and stress-test with it
 …

10. 10
Debugging
 Debugging is a very time-consuming process
 You do not create code while debugging
Avoid using debugger!
Read the printout instead

11. 11
Programming in Pairs
 If the implementation is too difficult for you…
 If you are tired…
 If the code is large…
 Try programming in pairs:
 One of the team members writes the code
 Another one is looking for mistakes
 This idea is from eXtreme Programming

12. 12
Last hour of the contest
 Your goal is to get “Accepted” for all
problems you have started
 Do not start new problems if you have “old”
ones
 If you do not have enough time for all
problems choose some of them

13. 13
Log of the contest
 Only for trainings
 Helps you to analyze the results of the contest
Time Member 1 Member 2 Member 3
30 Wrote a template Read A, B, C, D.
Wrote solution for
B
Read F, G, H, I
60 … … …
… … … …
300 … … …

14. 14
Thank you!
We wish you success in ACM
ICPC!