MO's Algorithm - Framework

Here's the MO's algorithm structure:

function moAlgorithm(arr, queries)
    B := floor(sqrt(n))
    sort queries by (floor(l / B), r)

    currentL := 0
    currentR := -1
    currentAnswer := initial value

    for each query (l, r, queryIndex)
        // Expand/shrink to reach [l, r]
        while currentR < r
            currentR := currentR + 1
            add(arr[currentR])
        while currentL > l
            currentL := currentL - 1
            add(arr[currentL])
        while currentR > r
            remove(arr[currentR])
            currentR := currentR - 1
        while currentL < l
            remove(arr[currentL])
            currentL := currentL + 1

        answers[queryIndex] := currentAnswer

    return answers

You implement $add$ and $remove$ based on what you're computing.