Problem - Range Sum Query Mutable

Given an integer array nums, implement:

• update(index, val): Update nums[index] to val
• sumRange(left, right): Return the sum of elements from left to right inclusive Example:

nums = [1, 3, 5]
sumRange(0, 2) → 9
update(1, 2)
sumRange(0, 2) → 8
``` You're solving the textbook segment tree application. 

Both operations must be efficient. Constraints: up to $3 \cdot 10^4$ elements, up to $3 \cdot 10^4$ operations.