LeetCode 304 Range Sum Query 2D - Immutable - Why Naive Fails

For each query, loop through all elements in the rectangle and sum them.

A rectangle can have up to $m \times n$ elements. With $q$ queries, that's $O(q \cdot m \cdot n)$.

For a $200 \times 200$ matrix with $10^4$ queries, you'd access $400$ million elements. Too slow.