\begin{algorithm}
        \caption{Counting Elements in a Given Interval}
        \begin{algorithmic}
        \INPUT a sequence $A$ of $n$ elements ranging from $0$ to $k$
        \OUTPUT a procedure that can count the number of elements in interval $[a..b]$
        \STATE let $C[0..k]$ be a new array initialized with all 0's
        \FOR{$i = 1$ \TO $n$}
            \STATE $C[A[i]] = C[A[i]] + 1$
        \ENDFOR
        \STATE \COMMENT{$C[i]$ now contains the number of elements equal to $i$}
        \FOR{$i = 1$ \TO $k$}
            \STATE $C[i] = C[i] + C[i-1]$
        \ENDFOR
        \STATE \COMMENT{$C[i]$ now contains the number of elements less than or equal to $i$}
        \STATE
        \PROCEDURE{IntervalCount}{$a, b$}
            \RETURN $C[b] - C[a-1]$
        \ENDPROCEDURE
        \STATE \COMMENT{count the number of $A$'s elements in interval $[a..b]$ within $O(1)$}
        \end{algorithmic}
        \end{algorithm}