Question

How to check whether a number is a perfect number in Rust

Answer 1

// If the sum of all factors of a number is equal to the number, then the number is perfect
 
// Factors of a number are numbers that divide the number evenly
    
// 6
// factors = 1, 2, 3
// 1 + 2 + 3 = 6

fn is_perfect(n: u64) -> bool {
    if n < 2 {
        return false;
    }

    let mut sum = 1; // 1 is always a divisor
    let limit = (n as f64).sqrt() as u64;

    for i in 2..=limit {
        if n % i == 0 {
            sum += i;
            let pair = n / i;
            if pair != i {
                sum += pair;
            }
        }
    }

    sum == n
}

fn main() {
    for num in 1..10000 {
        if is_perfect(num) {
            println!("{} is a perfect number", num);
        }
    }
}


/*
run:

6 is a perfect number
28 is a perfect number
496 is a perfect number
8128 is a perfect number

*/

 

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