Colombian Collegiate Programming League 2012 Problems

[AhmadKhatar]

Hi!
Does anybody know the algorithms used in the contest mentioned above?
I mean problems 12461 through 12470. I only need the names of the algorithms.
Thanks in advance!

[brianfry713]

12461 - Airplane - Probability theory.
12462 - Rectangle - I haven't solved it yet.
12463 - Little Nephew - Simple math.
12464 - Professor Lazy, Ph.D. - Simulation, GCD, rational numbers.
12465 - The Turanga Leela Problem - I haven't solved it yet.
12466 - Ancestors - I haven't solved it yet but you could call it graph theory.
12467 - Secret Word - String processing.
12468 - Zapping - Simple math, absolute value.
12469 - Stones - DP.
12470 - Tribonacci - I haven't solved it yet but you could try the matrix-power method.

[nupt-xxp]

yes, as brianfry713 says,i just plus that the 12467 can be solved by KMP.
and i don't know how to solve 12470,Could somebody tell me how to solve it?
maybe it's matrics , but i don't know its details,Could someone explain it to me ?
Please..
sorry for my bad english

[stubbscroll]

12465 - Number theory (number of divisors)
12466 - Topological sort, DP
12469 - Combinatorial game theory (win/loss-minimax with memoization)
12470 - Convert recurrence into matrix, fast matrix exponentiation

I think it's better to ask questions about individual problems in their own threads in order to keep this forum more tidy.

[AhmadKhatar]

yes, as brianfry713 says,i just plus that the 12467 can be solved by KMP.
and i don't know how to solve 12470,Could somebody tell me how to solve it?
maybe it's matrics , but i don't know its details,Could someone explain it to me ?
Please..
sorry for my bad english

Hi and thanks for your help!
I solved it using the recurrence attached at the bottom.
Then you can use fast exponentiation to find the answer. For example to find matrix F to the power of n (i.e. F(n)):
if ( n is 0 ){
return unit-matrix(i.e. I);
}
else if ( n is even ){
return F(n/2)*F(n/2);
}
else{
return F(n-1)*F(1);
}
Remember that at each step of the recursion you should use modulus. Otherwise the result will be an overflow.

[nupt-xxp]

yes, as brianfry713 says,i just plus that the 12467 can be solved by KMP.
and i don't know how to solve 12470,Could somebody tell me how to solve it?
maybe it's matrics , but i don't know its details,Could someone explain it to me ?
Please..
sorry for my bad english

Hi and thanks for your help!
I solved it using the recurrence attached at the bottom.
Then you can use fast exponentiation to find the answer. For example to find matrix F to the power of n (i.e. F(n)):
if ( n is 0 ){
return unit-matrix(i.e. I);
}
else if ( n is even ){
return F(n/2)*F(n/2);
}
else{
return F(n-1)*F(1);
}
Remember that at each step of the recursion you should use modulus. Otherwise the result will be an overflow.

Thanks , i solved it! And the picture you shows is wonderful !
Also i found another wonderful picture!

[nupt-xxp]

12461 - Airplane - Probability theory.
12462 - Rectangle - I haven't solved it yet.
12463 - Little Nephew - Simple math.
12464 - Professor Lazy, Ph.D. - Simulation, GCD, rational numbers.
12465 - The Turanga Leela Problem - I haven't solved it yet.
12466 - Ancestors - I haven't solved it yet but you could call it graph theory.
12467 - Secret Word - String processing.
12468 - Zapping - Simple math, absolute value.
12469 - Stones - DP.
12470 - Tribonacci - I haven't solved it yet but you could try the matrix-power method.

Now i'm thinking 12464,but i've no idea to solve it even you give the hints above.
a,b,n is so large and how to express a rational number ....
i'm puzzled and could someone tell me ?

[brianfry713]

On 12464 Try to solve the sample input with small n first. Code the rationals with two variables, one for the numerator and one for the denominator.

[nupt-xxp]

On 12464 Try to solve the sample input with small n first. Code the rationals with two variables, one for the numerator and one for the denominator.

think you !i solved it!