So I was solving this problem Keen Tree Calculation from the recent contest, I was not able to figure out why I was getting a runtime error on Test 11. After struggling for half a day, I decided look in other people's submission and I found out a team which faced the similar issue. The fix for the problem was to make a copy of vector and then to iterate on it rather than iterating on the original. Here I have linked my submissions Accepted , RTE . It would be of great help, if someone can explain why the latter doesn't work.

Thanks

Update: The problem occurs because i am iterating over a vector whose size changes during the iteration and thus it may be reallocated.