Problem - Count in Range

Given array $A$, answer: "How many elements in $A[l..r]$ have value in $[a, b]$?" Example: $A = [1, 5, 2, 6, 3, 7, 4]$ Query $(1, 5, 2, 5)$: elements in $[5, 2, 6, 3]$ with value in $[2, 5]$ are $5, 2, 3$ = count $3$.

Use the same persistent segment tree structure. Instead of finding $k$-th, count elements in a value range.