From f8dcb4ba16f3c34eb893d7d2c5ff78797609a73a Mon Sep 17 00:00:00 2001
From: "Dr. Matthias Ratajczak" <m.ratajczak@hzdr.de>
Date: Thu, 18 Aug 2022 20:44:53 +0200
Subject: [PATCH] add 12 (WIP)

---
 src/euler12/Cargo.toml  | 12 +++++++
 src/euler12/src/main.rs | 80 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+)
 create mode 100644 src/euler12/Cargo.toml
 create mode 100644 src/euler12/src/main.rs

diff --git a/src/euler12/Cargo.toml b/src/euler12/Cargo.toml
new file mode 100644
index 0000000..3d0a76a
--- /dev/null
+++ b/src/euler12/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "euler12"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
+[profile.release]
+lto = true
+
diff --git a/src/euler12/src/main.rs b/src/euler12/src/main.rs
new file mode 100644
index 0000000..aa2a16b
--- /dev/null
+++ b/src/euler12/src/main.rs
@@ -0,0 +1,80 @@
+use std::collections::{HashMap, HashSet};
+
+type Int = u64;
+
+fn main() {
+    let mut triangles = Triangle::new();
+    let mut factors_dict = HashMap::from([(1, vec![1])]);
+    loop {
+        let tn = triangles.next().unwrap();
+        print!("{tn}: ");
+        let factors = factorize(tn, &mut factors_dict);
+        if factors.len() > 500 {
+            println!("\n{tn}");
+            break;
+        } else {
+            println!("{}", factors.len());
+        }
+    }
+}
+
+fn factorize(x: Int, dict: &mut HashMap<Int, Vec<Int>>) -> HashSet<Int> {
+    let mut result = HashSet::from([x]);
+    let mut numbers_to_consider = HashSet::from([1..=(x / 2)]);
+    for i in .rev() {
+        if x % i == 0 {
+            result.insert(i);
+        }
+    }
+    // result.push(x);
+    result
+}
+
+struct Triangle {
+    last_result: Int,
+    last_number: Int,
+}
+
+impl Triangle {
+    fn new() -> Self {
+        Triangle {
+            last_result: 0,
+            last_number: 0,
+        }
+    }
+}
+
+impl Iterator for Triangle {
+    type Item = Int;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.last_number += 1;
+        self.last_result += self.last_number;
+        Some(self.last_result)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::factorize;
+    use crate::Triangle;
+
+    #[test]
+
+    fn test_factorize() {
+        assert_eq!(factorize(6), vec![1, 2, 3, 6]);
+        assert_eq!(factorize(28), vec![1, 2, 4, 7, 14, 28]);
+    }
+
+    #[test]
+    fn test_triangle() {
+        let mut t = Triangle::new();
+        assert_eq!(t.next().unwrap(), 1);
+        assert_eq!(t.next().unwrap(), 3);
+        assert_eq!(t.next().unwrap(), 6);
+        assert_eq!(t.next().unwrap(), 10);
+        assert_eq!(t.next().unwrap(), 15);
+        assert_eq!(t.next().unwrap(), 21);
+        assert_eq!(t.next().unwrap(), 28);
+    }
+}