package main
import (
"fmt"
"regexp"
)
func isBinary(s string) bool {
binary := regexp.MustCompile(`^[01]+$`)
return binary.MatchString(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
*/
// bool divisibleBy7(const std::string& s) {
func divisibleBy7(s string) bool {
remainder := 0
for _, c := range s {
remainder = (remainder*2 + int(c-'0')) % 7
}
return remainder == 0
}
func main() {
s := "00011100" // 28
if !isBinary(s) {
fmt.Println("Not a binary string")
return
}
if divisibleBy7(s) {
fmt.Println("Divisible by 7")
} else {
fmt.Println("Not divisible by 7")
}
}
/*
run:
Divisible by 7
*/
