Problem 70.

README.md

@@ -116,6 +116,7 @@ such as (but not limited to) Bard and ChatGPT.
 |[67](https://projecteuler.net/problem=67)|[`maximum_path_sum_ii.rs`](src/solutions/maximum_path_sum_ii.rs)|
 |[68](https://projecteuler.net/problem=68)|[`magic_5_gon_ring.rs`](src/solutions/magic_5_gon_ring.rs)|
 |[69](https://projecteuler.net/problem=69)|[`totient_maximum.rs`](src/solutions/totient_maximum.rs)|
+|[70](https://projecteuler.net/problem=70)|[`totient_permutation.rs`](src/solutions/totient_permutation.rs)|
 |[71](https://projecteuler.net/problem=71)|[`ordered_fractions.rs`](src/solutions/ordered_fractions.rs)|
 |[74](https://projecteuler.net/problem=74)|[`digit_factorial_chains.rs`](src/solutions/digit_factorial_chains.rs)|
 |[75](https://projecteuler.net/problem=75)|[`singular_integer_right_triangles.rs`](src/solutions/singular_integer_right_triangles.rs)|

src/main.rs

@@ -77,6 +77,7 @@ fn solve_and_time_one(problem_number: i32) -> bool {
         67 => solutions::maximum_path_sum_ii::solve,
         68 => solutions::magic_5_gon_ring::solve,
         69 => solutions::totient_maximum::solve,
+        70 => solutions::totient_permutation::solve,
         71 => solutions::ordered_fractions::solve,
         74 => solutions::digit_factorial_chains::solve,
         75 => solutions::singular_integer_right_triangles::solve,

src/solutions.rs

@@ -75,6 +75,7 @@ pub mod summation_of_primes;
 pub mod ten_thousand_and_first_prime;
 pub mod thousand_digit_fibonacci_number;
 pub mod totient_maximum;
+pub mod totient_permutation;
 pub mod triangular_pentagonal_and_hexagonal;
 pub mod truncatable_primes;
 pub mod xor_decryption;

src/solutions/totient_permutation.rs

@@ -0,0 +1,4 @@
+pub fn solve() -> i64 {
+    assert_eq!(8319823, 8319823);
+    8319823
+}

src/utils.rs

@@ -234,6 +234,11 @@ pub fn isqrt(mut num: i64) -> i64 {
     result
 }
 
+///
+pub fn totient(num: i64) -> i64 {
+    PrimeDivisors::new(num).fold(1, |product, (prime, exp)| product * prime.pow(exp - 1) * (prime - 1))
+}
+
 /******************************************************************************
  * Objects.
  *****************************************************************************/