Solve 44, 187 in rust

README.rst

@@ -88,7 +88,7 @@ Olivia's Project Euler Solutions
 |            | GraalPy 23.1+ |br|         |        | |CodeQL| |br|     |
 |            | Browser [#]_               |        | |PythonLint|      |
 +------------+----------------------------+--------+-------------------+
-| Rust       | 1.69+ |br|                 | 36     | |Rust| |br|       |
+| Rust       | 1.69+ |br|                 | 38     | |Rust| |br|       |
 |            | Browser [#]_               |        | |Rs-Cov| |br|     |
 |            |                            |        | |RustClippy|      |
 +------------+----------------------------+--------+-------------------+

docs/index.rst

@@ -226,7 +226,7 @@ Problems Solved
 +-----------+------------+------------+------------+------------+------------+------------+------------+
 |:prob:`145`|            |            |            |            |            |:py-d:`0145`|            |
 +-----------+------------+------------+------------+------------+------------+------------+------------+
-|:prob:`187`|            |            |            |            |            |:py-d:`0187`|            |
+|:prob:`187`|            |            |            |            |            |:py-d:`0187`|:rs-d:`0187`|
 +-----------+------------+------------+------------+------------+------------+------------+------------+
 |:prob:`206`|            |            |            |            |            |:py-d:`0206`|            |
 +-----------+------------+------------+------------+------------+------------+------------+------------+

docs/src/rust/p0044.rst

@@ -0,0 +1,20 @@
+Rust Implementation of Problem 44
+=================================
+
+View source code :source:`rust/src/p0044.rs`
+
+Includes
+--------
+
+- `math <./lib/math.html>`_
+
+Problem Solution
+----------------
+
+.. rust:fn:: pub fn p0044::p0044() -> utils::Answer
+
+.. literalinclude:: ../../../rust/src/p0044.rs
+   :language: rust
+   :linenos:
+
+.. tags:: figurate-number

docs/src/rust/p0187.rst

@@ -0,0 +1,20 @@
+Rust Implementation of Problem 187
+==================================
+
+View source code :source:`rust/src/p0187.rs`
+
+Includes
+--------
+
+- `primes <./lib/primes.html>`_
+
+Problem Solution
+----------------
+
+.. rust:fn:: pub fn p0187::p0187() -> utils::Answer
+
+.. literalinclude:: ../../../rust/src/p0187.rs
+   :language: rust
+   :linenos:
+
+.. tags:: factorization, prime-number, rust-iterator

rust/README.rst

@@ -85,6 +85,7 @@ Problems Solved
 -  ☒ `34 <./src/p0034.rs>`__
 -  ☒ `36 <./src/p0036.rs>`__
 -  ☒ `37 <./src/p0037.rs>`__
+-  ☒ `44 <./src/p0044.rs>`__
 -  ☒ `45 <./src/p0045.rs>`__
 -  ☒ `53 <./src/p0053.rs>`__
 -  ☒ `59 <./src/p0059.rs>`__
@@ -93,6 +94,7 @@ Problems Solved
 -  ☒ `76 <./src/p0076.rs>`__
 -  ☒ `77 <./src/p0077.rs>`__
 -  ☒ `87 <./src/p0087.rs>`__
+-  ☒ `187 <./src/p0187.rs>`__
 -  ☒ `357 <./src/p0357.rs>`__
 -  ☒ `836 <./src/p0836.rs>`__
 

rust/src/include/math.rs

@@ -83,3 +83,19 @@ where I: Copy + From<u8> + From<u64> + NumAssign + PartialOrd + CheckedMul + Deb
     }
     return answer;
 }
+
+pub fn triangle<I>(n: I) -> I where I: NumAssign + Copy {
+    let two = one::<I>() + one();
+    return n * (n + one()) / two;
+}
+
+pub fn pentagonal<I>(n: I) -> I where I: NumAssign + Copy {
+    let two = one::<I>() + one();
+    let three = two + one();
+    return n * (three * n - one()) / two;
+}
+
+pub fn hexagonal<I>(n: I) -> I where I: NumAssign + Copy {
+    let two = one::<I>() + one();
+    return n * (two * n - one());
+}

rust/src/include/problems.rs

@@ -8,6 +8,7 @@ use crate::p0027::p0027;
 use crate::p0034::p0034;
 use crate::p0036::p0036;
 use crate::p0037::p0037;
+use crate::p0044::p0044;
 use crate::p0045::p0045;
 use crate::p0053::p0053;
 use crate::p0059::p0059;
@@ -16,6 +17,7 @@ use crate::p0069::p0069;
 use crate::p0076::p0076;
 use crate::p0077::p0077;
 use crate::p0087::p0087;
+use crate::p0187::p0187;
 use crate::p0357::p0357;
 use crate::p0836::p0836;
 
@@ -52,6 +54,7 @@ pub fn get_problem<'b>(n: usize) -> Option<ProblemRef<'b>> {
         34 =>  Some(( &34, p0034, false)),
         36 =>  Some(( &36, p0036, false)),
         37 =>  Some(( &37, p0037, true)),
+        44 =>  Some(( &44, p0044, false)),
         45 =>  Some(( &45, p0045, false)),
         53 =>  Some(( &53, p0053, false)),
         59 =>  Some(( &59, p0059, false)),
@@ -60,6 +63,7 @@ pub fn get_problem<'b>(n: usize) -> Option<ProblemRef<'b>> {
         76 =>  Some(( &76, p0076, false)),
         77 =>  Some(( &77, p0077, false)),
         87 =>  Some(( &87, p0087, false)),
+        187 => Some((&187, p0187, false)),
         357 => Some((&357, p0357, true)),
         836 => Some((&836, p0836, false)),
         _ => None,

rust/src/lib.rs

@@ -13,6 +13,7 @@ pub mod p0027;
 pub mod p0034;
 pub mod p0036;
 pub mod p0037;
+pub mod p0044;
 pub mod p0045;
 pub mod p0053;
 pub mod p0059;
@@ -21,6 +22,7 @@ pub mod p0069;
 pub mod p0076;
 pub mod p0077;
 pub mod p0087;
+pub mod p0187;
 pub mod p0357;
 pub mod p0836;
 

rust/src/main.rs

@@ -30,6 +30,7 @@ pub mod p0027;
 pub mod p0034;
 pub mod p0036;
 pub mod p0037;
+pub mod p0044;
 pub mod p0045;
 pub mod p0053;
 pub mod p0059;
@@ -38,6 +39,7 @@ pub mod p0069;
 pub mod p0076;
 pub mod p0077;
 pub mod p0087;
+pub mod p0187;
 pub mod p0357;
 pub mod p0836;
 
@@ -83,6 +85,7 @@ seq!(N in 01..=20 {
 #[case::problem_34(34)]
 #[case::problem_36(36)]
 #[case::problem_37(37)]
+#[case::problem_44(44)]
 #[case::problem_45(45)]
 #[case::problem_53(53)]
 #[case::problem_59(59)]
@@ -91,6 +94,7 @@ seq!(N in 01..=20 {
 #[case::problem_76(76)]
 #[case::problem_77(77)]
 #[case::problem_87(87)]
+#[case::problem_187(187)]
 // #[case::problem_357(357)]
 #[case::problem_836(836)]
 fn test_problem(#[case] id: usize) -> Result<(), String> {

rust/src/p0044.rs

@@ -0,0 +1,44 @@
+/*
+Project Euler Problem 44
+
+Problem:
+
+Pentagonal numbers are generated by the formula, Pn=n(3n−1)/2. The first ten pentagonal numbers are:
+
+1, 5, 12, 22, 35, 51, 70, 92, 117, 145, ...
+
+It can be seen that P4 + P7 = 22 + 70 = 92 = P8. However, their difference, 70 − 22 = 48, is not pentagonal.
+
+Find the pair of pentagonal numbers, Pj and Pk, for which their sum and difference are pentagonal and D = ``|Pk − Pj|``
+is minimised; what is the value of D?
+*/
+use std::cmp::min;
+
+use crate::include::math::pentagonal;
+use crate::include::utils::Answer;
+
+
+fn is_pentagonal(x: u64) -> u64 {
+    let root = ((24 * x + 1) as f64).sqrt();
+    let iroot = root.round() as u64;
+    if iroot == root {
+        return 0;
+    }
+    if (1 + iroot) % 6 != 0 {
+        return 0;
+    }
+    return (1 + iroot) / 6;
+}
+
+pub fn p0044() -> Answer {
+    let mut d: u64 = 1_000_000_000_000;
+    let pentagonals = (1..2_500).map(pentagonal).collect::<Vec<u64>>();
+    for (idx, k) in pentagonals.iter().enumerate() {
+        for j in &pentagonals[idx..] {
+            if is_pentagonal(j + k) != 0 && is_pentagonal(k - j) != 0 {
+                d = min(d, (k - j).abs());
+            }
+        }
+    }
+    return Answer::Int(d.into());
+}

rust/src/p0045.rs

@@ -10,39 +10,28 @@ Hexagonal 	  	Hn=n(2n−1) 	      	1, 6, 15, 28, 45, ...
 
 It can be verified that T285 = P165 = H143 = 40755.
 */
+use crate::include::math::{hexagonal,pentagonal,triangle};
 use crate::include::utils::Answer;
 
-fn t(n: u64) -> u64 {
-    return n * (n + 1) / 2;
-}
-
-fn p(n: u64) -> u64 {
-    return n * (3 * n - 1) / 2;
-}
-
-fn h(n: u64) -> u64 {
-    return n * (2 * n - 1);
-}
-
 pub fn p0045() -> Answer {
     let mut t_idx: u64 = 286;
     let mut p_idx: u64 = 166;
     let mut h_idx: u64 = 144;
-    let mut t_val = t(t_idx);
-    let mut p_val = p(p_idx);
-    let mut h_val = h(h_idx);
+    let mut t_val = triangle(t_idx);
+    let mut p_val = pentagonal(p_idx);
+    let mut h_val = hexagonal(h_idx);
     while !(t_val == p_val && p_val == h_val) {
         while t_val < p_val || t_val < h_val {
             t_idx += 1;
-            t_val = t(t_idx);
+            t_val = triangle(t_idx);
         }
         while p_val < t_val || p_val < h_val {
             p_idx += 1;
-            p_val = p(p_idx);
+            p_val = pentagonal(p_idx);
         }
         while h_val < p_val || h_val < t_val {
             h_idx += 1;
-            h_val = h(h_idx);
+            h_val = hexagonal(h_idx);
         }
     }
     return Answer::Int(t_val.into());

rust/src/p0187.rs

@@ -0,0 +1,43 @@
+/*
+Project Euler Problem 187
+
+I was able to chain this with a previous problem. Probably a suboptimal
+solution because of it, but it felt prettier this way.
+
+I was able to add a short-circuited fail case to the is_prime() method, though
+
+Revision 1:
+
+Switched to a set comprehension with caching. This means that I can remove it
+from the slow list.
+
+Problem:
+
+A composite is a number containing at least two prime factors. For example,
+15 = 3 × 5; 9 = 3 × 3; 12 = 2 × 2 × 3.
+
+There are ten composites below thirty containing precisely two, not necessarily
+distinct, prime factors: 4, 6, 9, 10, 14, 15, 21, 22, 25, 26.
+
+How many composite integers, n < 10**8, have precisely two, not necessarily
+distinct, prime factors?
+*/
+use std::collections::HashSet;
+
+use crate::include::primes::primes_until;
+use crate::include::utils::Answer;
+
+pub fn p0187() -> Answer {
+    let ten_8: u64 = 10_u64.pow(8);
+    let cached_primes: Vec<u64> = primes_until::<u64>(ten_8 / 2 + 1).collect();
+    let mut seen: HashSet<u64> = HashSet::new();
+    for &y in cached_primes.iter() {
+        for &x in cached_primes.iter() {
+            if x >= ten_8 / y {
+                break;
+            }
+            seen.insert(x * y);
+        }
+    }
+    return Answer::Int((seen.len() as u64).into());
+}