Tldr:
Can't fucking figure out why I'm the only one who can't solve a DP problem in code, when me and friends use the same idea and no one knows why only mine doesn't work...

We are given a task to solve a problem using DP. My friends write their code with the same idea as a solution. Copying the code is not allowed. I follow the same idea but my code won't work. Others look into it, in case they find errors. They can't find any.

The problem (for reference):
Given a fixed list of int's a = (a_1,a_2,...,a_n) and b = (b_1,b_2,...,b_n), a_i and b_i >= 0, a.length == b.length
We want to maximize the sum of a_i's chosen. Every a_i is connected with the b_i at the same index. b_i tells us how many indexes of a we have to skip if choosing the corresponding a_i, so list index of b_i + b_i's value + 1 would be the position of the next a_i available.

The idea:
Create a new list c with same length as a (or b).
Begin at the end of c and save a_n at the same position in c. Iterate backwards through c and at each position add the max value of all previously saved values of c (with regards to the b_i-restriction) with the current a_i, else a_i + 0 if the b_i-resctriction goes beyond the list.
Return the max value of c.

How does that not work for me but for the others?? Funny enough, a few given samples work with my code. I'm questioning my coding ability...