Editing 2015 Open Bronze Problem 2 Bessie Gets Even (section)

== Solution ==
This problem can be solved using a technique known as dynamic programming.

Firstly, for each number between 1 to 10, we count the frequency of its occurrence in the list. Let's denote this frequency as freq[i].

We can then create a 2D dynamic programming table, dp[i][j], where dp[i][j] represents the number of ways to make a sum of j using the first i numbers. We initially set dp[0][0] to 1 since there is only one way to create a sum of 0, that is by taking no numbers at all.

Then, for each number i from 1 to 10, we perform the following steps:

* We create a temporary copy of the DP table.
* We then iterate through all possible sums j from 0 to 20. For each sum, we consider adding k copies of the current number i, where k can range from 0 to freq[i]. For each valid k, we add the number of ways to form the sum j - k * i (from the previous set of numbers) to dp[i][j].
* After we've finished processing the current number i, we copy the temporary DP table back to the original one.

Finally, the answer to the problem is dp[10][0], since we want to count the number of ways to form an even sum (which is 0 modulo 2).