memory overflow

My reference has 430 words and the hypothesis has 498 words.
I have already figured out the following:
In the getStepList method, x and y never reach 0 at the same time. If x = 0 then y ~ 250 and if y = 0 then x is way below 0.
Then an infinite number of "d" are appended until the memory overflows but there is no error massage.

How can I fix this problem?