How to choose and arrange candidates into the rooms in the contest? Is the arrangement random, or obeying a rule / convention?

I had a process of practicing and trying to move from a newbie to a candidate master, but I realized that I was still stopping at D-E div.2 (difficulty about 2300). Now, I want to improve more so that I can at least achieve International Master or Grandmaster qualifications. Can you give me some suggestions?

I have a difficulty problem. Let F [n] be the number of positive integer divisors of the integer n. for example F [4] = 3 because 4 has 3 divisors which is {1,2,4}. Give two positive integers a and b (a <b; 1<=a<b<10^12). Calculate F[a] + F[a+1] + ... + F[b]. INPUT 2 5 OUTPUT 9 PLEASE HELP ME. THANK YOU SO MUCH

I want to create a competition with new problems not found on codeforces for my group, but I don't know how to do it. Please help me

There are M gifts and N students. Count the dividing numbers so that the number of gifts from the following student is not greater than the amount of the previous student's gift

input 3 2 output 2

explain : There are 2 ways to choose : (3;0) and (2;1)

for real numbers N(n<=2000), Find the longest real number array a[1], a[2], ..., a[m] such that the sum and product of that real number array is equal to N: a[1]+a[2]+...+a[m]=a[1].a[2]. ... . a[m] = N

here my code: http://ideone.com/2CsXul but it WA if n>=100

Sorry this is my first time writing blog