feat(problem): 42 - coded triangle numbers

readme.md

@@ -11,7 +11,7 @@ I originally started the challenge in [the-honk](https://github.com/newtykins/th
 
 ## Challenge Completion
 
-### <!-- completed -->17<!-- completed --> out of 100 public challenges completed.
+### <!-- completed -->18<!-- completed --> out of 100 public challenges completed.
 
 - [x] 1 - [Multiples of 3 or 5](src/bin/1.rs)
 - [x] 2 - [Even Fibonacci numbers](src/bin/2.rs)
@@ -54,7 +54,7 @@ I originally started the challenge in [the-honk](https://github.com/newtykins/th
 - [ ] 39 - Integer right triangles
 - [ ] 40 - Champernowne's constant
 - [ ] 41 - Pandigital prime
-- [ ] 42 - Coded triangle numbers
+- [x] 42 - [Coded triangle numbers](src/bin/42.rs)
 - [ ] 43 - Sub-string divisibility
 - [ ] 44 - Pentagon numbers
 - [ ] 45 - Triangular, pentagonal, and hexagonal

src/bin/22.rs

@@ -24,7 +24,7 @@ fn name_score(name: String, position: usize) -> usize {
     let mut letter_sum: usize = 0;
 
     for char in name.chars() {
-        // Letters start in ASCII at 65
+        // Capital letters start in ASCII at 65
         letter_sum += (char as usize) - 64;
     }
 

src/bin/42.rs

@@ -0,0 +1,57 @@
+/*
+Problem 42 - Coded triangle numbers
+
+The  n  th  term of the sequence of triangle numbers is given by,  t n   = ½ n ( n +1); so the first ten triangle numbers are:
+1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...
+By converting each letter in a word to a number corresponding to its alphabetical position and adding these values we form a word value. For example, the word value for SKY is 19 + 11 + 25 = 55 =  t  10 . If the word value is a triangle number then we shall call the word a triangle word.
+Using  words.txt  (right click and 'Save Link/Target As...'), a 16K text file containing nearly two-thousand common English words, how many are triangle words?
+*/
+
+use regex::Regex;
+use std::{fs, ops::Div};
+
+fn read_words() -> Vec<String> {
+    return fs::read_to_string(euler::resources_path().join("p042_words.txt"))
+        .unwrap()
+        .split(",")
+        .map(|name| {
+            Regex::new("\"")
+                .unwrap()
+                .replace_all(name, "")
+                .to_string()
+                .to_lowercase()
+        })
+        .collect::<Vec<String>>();
+}
+
+fn is_triangle_number(number: usize) -> bool {
+    let solution = (((8 * number + 1) as f64).sqrt() - 1.0).div(2.0);
+
+    return solution.fract() == 0.0 && solution > 0.0;
+}
+
+fn count_triangle_words(words: Vec<String>) -> usize {
+    let mut count: usize = 0;
+
+    for word in words {
+        let mut sum = 0;
+
+        for char in word.chars() {
+            // Lowercase letters start in ASCII at 97
+            sum += (char as usize) - 96;
+        }
+
+        if is_triangle_number(sum) {
+            count += 1;
+        }
+    }
+
+    return count;
+}
+
+fn main() {
+    let words = read_words();
+    let count = count_triangle_words(words);
+
+    println!("Out of nearly 2000 common English words, {count} are triangle words!");
+}