Question

How to check if a string contains only 0 and 1 and is divisible by 7 in Scala

Answer 1

import scala.util.matching.Regex

def isBinary(s: String): Boolean = {
  val binary: Regex = "^[01]+$".r
  
  binary.matches(s)
}

/*
In decimal: reading "123" means
remainder = remainder * 10 + digit

In binary: reading "1011" means
remainder = remainder * 2 + bit
*/

/*
0   (0*2 + 0) % 7   0
0   (0*2 + 0) % 7   0
0   (0*2 + 0) % 7   0
1   (0*2 + 1) % 7   1
1   (1*2 + 1) % 7   3
1   (3*2 + 1) % 7   0
0   (0*2 + 0) % 7   0
0   (0*2 + 0) % 7   0
*/

def divisibleBy7(s: String): Boolean = {
  var remainder = 0

  for (c <- s) {
    remainder = (remainder * 2 + (c - '0')) % 7
  }

  remainder == 0
}

@main def main(): Unit = {
  val s = "00011100" // 28

  if (!isBinary(s)) {
    println("Not a binary string")
    return
  }

  if (divisibleBy7(s)) {
    println("Divisible by 7")
  } else {
    println("Not divisible by 7")
  }
}




/*
run:

Divisible by 7

*/

 

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