Question

How to sum the digit of a factorial of a number in Rust

Answer 1

fn sum_digits(mut num: i64) -> i32 {
    let mut sum = 0;
    
    while num != 0 {
        sum += (num % 10) as i32;
        num /= 10;
    }
    sum
}

fn factorial(n: i64) -> i64 {
    if n == 1 || n == 0 {
        return 1;
    }
    n * factorial(n - 1)
}

fn main() {
    let number = 9;
    let result = factorial(number);

    println!("factorial = {}", result);
    println!("sum digits = {}", sum_digits(result));
}


     
/*
run:
  
factorial = 362880
sum digits = 27
    
*/

 

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