Hackerrank: AND Product Solution in Ocaml

AND product

Problem Statement

You will be given two intergers A and B. You are required to compute the bitwise AND amongst all natural numbers lying between A and B, both inclusive.

Input Format

First line of the input contains T, the number of testcases to follow.
Each testcase in a newline contains A and B separated by a single space.

Constraints

1 <= T <= 200
0 <= A <= B <= 2^32

Output Format

Output one line per test case with the required bitwise AND

let read_line_int () =
  let line = read_line () in
  let lst = Str.split (Str.regexp " ") line in
  let lst_int = List.map int_of_string lst in
  let arr = Array.of_list lst_int in
  arr
;;


let number_of_bits n =
  let rec num_of_bits count n =
    match n with
    | 0 -> count
    | n -> num_of_bits (count + 1) (n lsr 1)
  in
    num_of_bits 0 n ;;


let rec process result a b =
  let n_bits_a = number_of_bits a
  and n_bits_b = number_of_bits b in
  match n_bits_a = n_bits_b with
  | false -> result
  | true ->
    let m = 1 lsl (n_bits_a - 1) in
    process (result + m) (a - m) (b - m)
;;

let process_main a b =
  process 0 a b ;;



(* main part *)

let num_case = read_int () ;;

for i = 1 to num_case do
  let arr = read_line_int () in
  let result = process_main arr.(0) arr.(1) in
  Printf.printf "%d\n" result
done;;