Read Statement

Read the full problem at the link above. You need to count paths with length in the range $[k_1, k_2]$. Both bounds are inclusive. The constraints are similar to Fixed-Length Paths I, so you need an $O(n \log n)$ solution. Brute force checking all pairs and filtering by length will not work. Think about how to adapt the previous approach.

Instead of checking $d_1 + d_2 = k$, what range should $d_2$ be in?

Space complexity is $O(n)$ for the data structures used.