Hello. I've doing a problem on poj.com ( link : http://poj.org/problem?id=1195 )

The main idea of the problem is that we are given a S * S grid and there is 2 kind of operations.

Operation 1 : Change the cell x, y by adding a certain value A.

Operation 2 : Answer the sum of the rectangle which is defined by the two points; top leftmost : (l, b), bottom rightmost (r, t)

So obviously we need a 2D Binary Indexed Tree (because of operation 1). I tried to implement a 2D Segment Tree, but I'm getting a TLE.

Can someone help me figure out why ? Are Segment Trees not efficient here or my implementation of 2D Segment Tree is just bad ?

Link to my C++ code (getting TLE): http://pastebin.com/KA3UXm3N