can anyone provide the link for the questions of codenation republic contest for practice??

Represent the whole scenario as permutation of numbers from 1 to N(Bag has balls numbered from 1 to N and permutation represents which ball is picked in which move).Now if a permutation has answer K, then there are K winning positions in that permutation and each position contributes 1 to the answer for that permutation. So I translated the same to contribution of each position in all permutations. For position i, contribution is number of ways that position is ‘a’ winning position.So number of ways are :

nCi*(i-1)!*(n-i)! = (n! / i)

So for each i, we add the respective term to the answer ,and at the end divide whole sum by n! to get the expectation (total permutations possible are n!).

bro can you explain more clearly??

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Why is nCi being multiplied??

Or simply, it’s sigma(1*i^-1) right?

Because for every (i) you just have only i position to place that particular number .So to choose i places total of n places you multiply with nci.Lets understand with an example suppose you have n=10 and at currently you need to find for the 4 th position so at right you have( n-i) numbers so you need to take their all positions .Now on the left you have (i-1) position so you take their factorial now you need to put 4 in such a way so that it will always be in winning position so you have only 4 places in which your 4 will be at winning position so you just multiply with (nci) also…

HI can you please explain me how to do the first i was getting WA in that thanks

i solved the second problem in like 25 mins completely coded the 3rd problem went to try test case. error . variable name was wrong. corrected the var name , went to see test case all correct and then before i hit the submit button time was out.

easy one just make a function isprime which as name suggests returns true if a number is prime else false

like isprime(7) = true

isprime(10) false

now decompose a number in its canonical form

100 = 2^2 * 5^2

if the number of primes in canonical form is more than 1 print(NO)

solution

if n==1:

print(“No”)

if n==2:

print(“YES”)

else:

canonical_form = get_canonical(n)

if len(canonical_form) > 1:

print(NO)

else if isprime(canonical_form prime’s power + 1):

print(“YES”)

else:

print(“NO”)

Hey thanks but Can you explain me why “number of primes in canonical form is more than 1 print(NO)” i dont get that.

Given a number of the form P_{1}^{a}.P_{2}^{b}..., then what are the total factors? By using basic combinatorics it is (a+1).(b+1)... So, If the canonical form has more than 2 primes, then total number of factors is definately not a prime because it has atleast two factors which are not 1 or the number itself. However, if there is only one prime in the canonical form you have to put an additional prime check on a+1.

Oh okay wowww really great explanation man Thanks alot! Also did u do the 3 question?

However, I think this question can be solved using a slightly simple approach. You can count the total number of factors of a number in sqrt(N). Then check if this number is a prime, build a Linear Sieve in the pre-processing step.

Nah. I didn’t appear for the test besides I am a Noob in CP.

I did that thats why it was giving WA idk

You need to find all the factors of N in sqrt(N) time… put it in an array… then find the length of the array and print if the length is prime or not

How did you find the P for it ?

I did that too but idk WA :(((

I guess it’s the flow error… send the code if you have. I got AC for what I said above