first :here is your accepted code ,I just add a wrapper function called bootstrap and some few changes in recursions like change return with yield and add @boostrap decorator above any recursion function, you can search about bootstrap wrapper in codeforces blogs. second : I advice you to use bottom up segment tree not recursive version because python is very bad about resolving recursions as its stack not efficient ,here is my accepted code and see the difference in time execution between my code and your recursive code.