Introduction - If you have any usage issues, please Google them yourself
Let us consider the following problem to understand Segment Trees.
We have an array arr[0 . . . n-1]. We should be able to
1 Find the sum of elements from index l to r where 0 <= l <= r <= n-1
2 Change value of a specified element of the array to a new value x. We need to do arr[i] = x where 0 <= i <= n-1.