Digit Factorials

// Answer: 40730

// Authored by: Tim Varley 💘
// Assisted-by: Grok Code Fast via Crush 💘 <crush@charm.land>

#include <iostream>
#include <vector>
#include <string>

long long digit_factorials() {
    std::vector<long long> fact(10,1);
    for(int i=2; i<10; i++) fact[i] = fact[i-1] * i;
    long long sum = 0;
    for(long long i=10; i<10000000; i++) {
        std::string s = std::to_string(i);
        long long sf = 0;
        for(char c : s) sf += fact[c-'0'];
        if(sf == i) sum += i;
    }
    return sum;
}

#if ! defined UNITTEST_MODE
int main(int argc, char const *argv[]) {
    std::cout << digit_factorials() << std::endl;
}
#endif // UNITTEST_MODE

package org.tvarley.euler.solutions;

import org.tvarley.euler.Solution;

public class Solution034 implements Solution {
  public String solve() {
    long[] fact = new long[10];
    fact[0] = 1;
    for (int i = 1; i < 10; i++) fact[i] = fact[i-1] * i;
    long sum = 0;
    for (int i = 10; i < 10000000; i++) {
      if (isSumFact(i, fact)) sum += i;
    }
    return Long.toString(sum);
  }

  private boolean isSumFact(int n, long[] fact) {
    int s = 0;
    int temp = n;
    while (temp > 0) {
      s += fact[temp % 10];
      temp /= 10;
    }
    return s == n;
  }
}

module.exports = {
  answer: () => {
    const fact = [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880];
    function sumFactDig(n) {
      let sum = 0;
      while (n > 0) {
        sum += fact[n % 10];
        n = Math.floor(n / 10);
      }
      return sum;
    }
    let total = 0;
    for (let i = 10; i < 10000000; i++) {
      if (sumFactDig(i) === i) total += i;
    }
    return total;
  }
};

def solve():
    """
    Digit Factorials
    145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145.

    Find the sum of all numbers which are equal to the sum of the factorial of their digits.

    Note: As 1! = 1 and 2! = 2 are not sums they are not included.
    https://projecteuler.net/problem=34
    """
    import math
    fact = [math.factorial(i) for i in range(10)]
    total = 0
    # Upper limit: 9! * 7 = 2540160, 7 digits; 9! * 8 would be more but 8 digits > sum
    for n in range(10, 2540161):
        if sum(fact[int(d)] for d in str(n)) == n:
            total += n
    return total

package main

import "fmt"

import "strconv"

func fact(n int) int {
  if n == 0 {
    return 1
  }
  return n * fact(n-1)
}

func main() {
  facts := make([]int, 10)
  for i := 0; i < 10; i++ {
    facts[i] = fact(i)
  }
  sum := 0
  for n := 3; n < 100000; n++ {
    s := strconv.Itoa(n)
    total := 0
    for _, c := range s {
      total += facts[int(c-'0')]
    }
    if total == n {
      sum += n
    }
  }
  fmt.Println(sum)
}

// Answer: 40730

pub fn digit_factorials() -> u64 {
    let fact = [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880];
    let mut sum = 0;
    for n in 10..(362880 * 7) {
        let mut s = 0;
        let mut m = n;
        while m > 0 {
            s += fact[(m % 10) as usize];
            m /= 10;
        }
        if s == n {
            sum += n as u64;
        }
    }
    sum
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn euler_034() {
        assert_eq!(digit_factorials(), 40730);
    }
}