Method 1

This is a classic difference array problem. Increase the total brightness by $B$ at $A$ and decrease it by $B$ at $A + L$.

Time complexity

$\mathcal{O}(N)$

Space complexity

$\mathcal{O}(N)$

Method 2

Since there are a maximum of $10^7$ seconds in a show but $10^4$ fireworks, we don’t need such a big array that will mainly be empty. We can use coordinate compression to speed up the program and to reduce memory usage. However, both methods pass. Use a map as the difference array.

Time complexity

$\mathcal{O}(M\log M)$

Space complexity

$\mathcal{O}(M)$

Problem

Read the problem.