From caeaa98e9f31c2124f251a5da7c6496d9175f165 Mon Sep 17 00:00:00 2001
From: "Dr. Matthias Ratajczak" <m.ratajczak@hzdr.de>
Date: Tue, 9 Aug 2022 20:29:38 +0200
Subject: [PATCH] add solution for 50

---
 euler50/Cargo.toml  |  12 +++++
 euler50/src/main.rs | 113 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 125 insertions(+)
 create mode 100644 euler50/Cargo.toml
 create mode 100644 euler50/src/main.rs

diff --git a/euler50/Cargo.toml b/euler50/Cargo.toml
new file mode 100644
index 0000000..df1b20a
--- /dev/null
+++ b/euler50/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "euler50"
+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
+opt-level = 3
diff --git a/euler50/src/main.rs b/euler50/src/main.rs
new file mode 100644
index 0000000..c3866f5
--- /dev/null
+++ b/euler50/src/main.rs
@@ -0,0 +1,113 @@
+use std::collections::HashSet;
+
+// you will probably need to incrase the stack limit
+// $ ulimit -s
+// $ ulimit -s 32768
+
+type Int = i64;
+const MIN_VALUE: Int = 2;
+const MAX_VALUE: Int = 1_000_000;
+const SIZE: usize = (MAX_VALUE - MIN_VALUE) as usize;
+type Array = [bool; SIZE];
+
+fn main() {
+    println!("Getting prime numbers up to {}", MAX_VALUE);
+    let primes = Primes::from_array(get_prime_numbers_array());
+    println!("Starting to iterate ...");
+    let result = find_using_iter(&primes).unwrap();
+    println!(
+        "{:?} / sum: {} / len: {}",
+        result,
+        sum_of_vector(result),
+        result.len()
+    );
+}
+
+fn get_prime_numbers_array() -> Array {
+    // Sieve of Eratosthenes
+    let mut result = [true; SIZE];
+    for number_to_check in MIN_VALUE..(MAX_VALUE / 2) {
+        let mut last_number = number_to_check;
+        loop {
+            let current_number = last_number + number_to_check;
+            if current_number >= MAX_VALUE {
+                break;
+            }
+            result[(current_number - MIN_VALUE) as usize] = false;
+            last_number = current_number;
+        }
+    }
+    result
+}
+
+fn sum_of_vector(vector: &[Int]) -> Int {
+    vector.iter().sum()
+}
+
+struct Primes {
+    vector: Vec<Int>,
+    set: HashSet<Int>,
+}
+
+struct PrimesIter<'a> {
+    primes: &'a Primes,
+    current_min: usize,
+    current_len: usize,
+}
+
+impl<'a> Iterator for PrimesIter<'a> {
+    type Item = &'a [Int];
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let result = &self.primes.vector[self.current_min..(self.current_min + self.current_len)];
+        if result.iter().sum::<Int>() > MAX_VALUE {
+            self.decrement_search_length();
+            return self.next();
+        }
+        if self.current_min + self.current_len < self.primes.vector.len() {
+            self.current_min += 1;
+        } else {
+            self.decrement_search_length();
+        }
+        Some(result)
+    }
+}
+
+impl<'a> PrimesIter<'a> {
+    fn decrement_search_length(&mut self) {
+        self.current_min = 0;
+        self.current_len -= 1;
+        println!("{}", self.current_len);
+    }
+}
+
+impl Primes {
+    fn iter(&self) -> PrimesIter {
+        PrimesIter {
+            primes: self,
+            current_min: 0,
+            current_len: self.vector.len(),
+        }
+    }
+
+    fn from_array(array: Array) -> Primes {
+        let mut vector = Vec::new();
+        let mut set = HashSet::new();
+        for number in MIN_VALUE..MAX_VALUE {
+            if array[(number - MIN_VALUE) as usize] {
+                vector.push(number);
+                set.insert(number);
+            }
+        }
+        Primes { vector, set }
+    }
+}
+
+fn find_using_iter(primes: &'_ Primes) -> Option<&'_ [Int]> {
+    for subvector in primes.iter() {
+        if primes.set.contains(&sum_of_vector(subvector)) {
+            return Some(subvector);
+        }
+    }
+    None
+}