Hi. I have encountered this problem recently and didn't know how to approach it.
We want to construct compounds with these properties:
Chas 4 links and can bond with eitherC,HorIHcan bond withConly through 1 linkIcan bond withConly through 2 links- there is no atom with one or more free links
For example, H-C=C is not a compound because the middle C needs another link and the right one 2 more.
Two compounds are different if the numbers of C, H or I differ.
Now we define the mass of a compound as 5 * no. of C + 3 * no. of I + no. of H.
Task
Given 30 <= N <= 100000, find how many compounds with mass N there are with at least one C, I and H.
Example:
Input: N = 40
Output: 3
Explanation
These are the only possible compounds with mass 40:




