Check digitorial permutation

Math Counting

46.5% acceptance

Mar 15, 2026

You are given an integer n. A number is digitorial if the sum of factorials of its digits equals the number itself. Determine whether any permutation of n (not starting with zero) forms a digitorial number. Return true if such a permutation exists, otherwise false.

Solution

Rust

Time O(n log n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn is_digitorial_permutation(n: i32) -> bool {
    let mut digits = Vec::new();
    let mut tmp = n;
    while tmp > 0 {
      digits.push((tmp % 10) as u64);
      tmp /= 10;
    }
    digits.sort();

    let factorials: [u64; 10] = [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880];

    let digit_sum: u64 = digits.iter().map(|&d| factorials[d as usize]).sum();

    let mut sum_digits = Vec::new();
    let mut s = digit_sum;
    if s == 0 { return false; }
    while s > 0 {
      sum_digits.push(s % 10);
      s /= 10;
    }
    sum_digits.sort();

    digits == sum_digits
  }
}