echo/examples/algos/digits.echo at main · csfh/echo · GitHub

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; Digit tricks — sum of digits, reverse digits, numeric palindrome.
; Run: xo run examples/algos/digits.echo

/ std/io
/ std/str

$ abs = (n) {
    ? n < 0 {
        ^ 0 - n
    }
    ^ n
}

$ digit_sum = (n) {
    ~ x = abs(n)
    ~ s = 0
    * x > 0 {
        ~ s = s + x % 10
        ~ x = x / 10
    }
    ^ s
}

$ reverse_digits = (n) {
    ~ neg = n < 0
    ~ x = abs(n)
    ~ r = 0
    * x > 0 {
        ~ r = r * 10 + x % 10
        ~ x = x / 10
    }
    ? neg {
        ^ 0 - r
    }
    ^ r
}

$ is_palindrome = (n) {
    ^ n == reverse_digits(n)
}

; Digital root: repeated digit_sum until a single digit (equiv. n mod 9).
$ digital_root = (n) {
    ~ x = abs(n)
    ? x == 0 {
        ^ 0
    }
    * x >= 10 {
        ~ x = digit_sum(x)
    }
    ^ x
}

io.print(str.from_int(digit_sum(12345)))
io.print(str.from_int(digit_sum(0)))
io.print(str.from_int(reverse_digits(1234)))
io.print(str.from_int(reverse_digits(-120)))
io.print(str.from_int(is_palindrome(12321)))
io.print(str.from_int(is_palindrome(1234)))
io.print(str.from_int(digital_root(9999)))
io.print(str.from_int(digital_root(38)))

\ digit_sum, reverse_digits, is_palindrome, digital_root, abs