Update: The problem was my 'decompose' function. Its return type was 'int' though I didn't return anything, so I changed it into 'void' and I got AC. Weird but worked.

I tried to solve this problem using HLD and Segment Tree. I didn't find LCA explicitly rather used HLD.

Code: https://pastebin.ubuntu.com/p/BfxMZH9hz3/

This solution gives runtime error. I can't find any reason for this kind of verdict.

I have already read this blog but couldn't understand why my code isn't working.

Can anyone help me?