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src/euler26/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "euler26"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+itertools = "0.14.0"
+rug = "*"

src/euler26/src/main.rs

@@ -0,0 +1,89 @@
+use itertools::Itertools;
+use rug::Float;
+
+const PRECISION: u32 = 16_192;
+const MIN: usize = 2;
+const MAX: usize = 1_000;
+
+fn main() {
+    let mut largest_number = 1;
+    let mut largest_len = 1;
+
+    for number in MIN..MAX {
+        println!("{number}");
+        if let Some(value) = find_cycle_length(number as f64) {
+            if value > largest_len {
+                largest_len = value;
+                largest_number = number;
+            }
+        }
+    }
+
+    println!("{largest_number}: {largest_len}");
+}
+
+fn find_cycle_length(number: f64) -> Option<usize> {
+    let n = Float::with_val(PRECISION, 1.);
+    let d = Float::with_val(PRECISION, number);
+    let r = n / d;
+    let s = r.to_string();
+
+    let max_length = s.len() / 3;
+
+    let s = sanitize_string(s);
+
+    for skip in 0..max_length {
+        for length in 1..max_length {
+            let chunks = s.chars().skip(skip).chunks(length);
+            let mut iter = chunks.into_iter();
+
+            let first: String = iter.next().unwrap().collect();
+            let second: String = iter.next().unwrap().collect();
+            let third: String = iter.next().unwrap().collect();
+
+            if first == second && second == third {
+                return Some(length);
+            }
+        }
+    }
+    None
+}
+
+fn sanitize_string(s: String) -> String {
+    let exponent = s.chars().last().unwrap().to_digit(10).unwrap();
+
+    let mut s: String = s
+        .chars()
+        .take_while(|c| !c.is_ascii_lowercase())
+        .filter(|c| *c != '.')
+        .collect();
+
+    let add_leading_zeros = exponent - 1;
+    for _ in 0..add_leading_zeros {
+        s.insert(0, '0');
+    }
+    s
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::find_cycle_length;
+
+    #[test]
+    fn case_3() {
+        let result = find_cycle_length(3.);
+        assert_eq!(result, Some(1))
+    }
+
+    #[test]
+    fn case_6() {
+        let result = find_cycle_length(6.);
+        assert_eq!(result, Some(1))
+    }
+
+    #[test]
+    fn case_7() {
+        let result = find_cycle_length(7.);
+        assert_eq!(result, Some(6))
+    }
+}