Problem - Range Addition

You have an array of length $n$ initialized to zeros. You're given $k$ update operations. Each operation adds a value $val$ to all elements from index $start$ to $end$ inclusive.

Return the final array. You're solving the textbook difference array problem. With $k$ updates and length $n$, naive approach is $O(kn)$. With difference arrays, it's $O(k + n)$. Read the problem carefully.