andu9's blog

By andu9, history, 19 months ago, In English

Hi. I have encountered this problem recently and didn't know how to approach it.

We want to construct compounds with these properties:

  • C has 4 links and can bond with either C, H or I
  • H can bond with C only through 1 link
  • I can bond with C only 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:

Poza

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