From a5b363793384136d966ceb8e5375778d20df3d47 Mon Sep 17 00:00:00 2001
From: "exercism-solutions-syncer[bot]"
 <211797793+exercism-solutions-syncer[bot]@users.noreply.github.com>
Date: Tue, 27 Jan 2026 09:48:40 +0000
Subject: [PATCH] [Sync Iteration] rust/list-ops/2

---
 solutions/rust/list-ops/2/Cargo.toml |   9 ++
 solutions/rust/list-ops/2/src/lib.rs | 188 +++++++++++++++++++++++++++
 2 files changed, 197 insertions(+)
 create mode 100644 solutions/rust/list-ops/2/Cargo.toml
 create mode 100644 solutions/rust/list-ops/2/src/lib.rs

diff --git a/solutions/rust/list-ops/2/Cargo.toml b/solutions/rust/list-ops/2/Cargo.toml
new file mode 100644
index 00000000..2637d4f1
--- /dev/null
+++ b/solutions/rust/list-ops/2/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "list_ops"
+version = "0.1.0"
+edition = "2024"
+
+# Not all libraries from crates.io are available in Exercism's test runner.
+# The full list of available libraries is here:
+# https://github.com/exercism/rust-test-runner/blob/main/local-registry/Cargo.toml
+[dependencies]
diff --git a/solutions/rust/list-ops/2/src/lib.rs b/solutions/rust/list-ops/2/src/lib.rs
new file mode 100644
index 00000000..c19eb815
--- /dev/null
+++ b/solutions/rust/list-ops/2/src/lib.rs
@@ -0,0 +1,188 @@
+/// Gibt jedes Element von a und dann jedes Element von b zurück (ohne chain)
+pub fn append<I, J>(a: I, b: J) -> Append<I, J>
+where
+    I: Iterator,
+    J: Iterator<Item = I::Item>,
+{
+    Append { a, b }
+}
+
+pub struct Append<I, J> {
+    a: I,
+    b: J,
+}
+
+impl<I, J> Iterator for Append<I, J>
+where
+    I: Iterator,
+    J: Iterator<Item = I::Item>,
+{
+    type Item = I::Item;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.a.next().or_else(|| self.b.next())
+    }
+}
+
+/// Kombiniert alle Elemente aus allen verschachtelten Iteratoren zu einem flachen Iterator (ohne flatten)
+pub fn concat<I>(nested_iter: I) -> Concat<I>
+where
+    I: Iterator,
+    I::Item: Iterator,
+{
+    Concat {
+        outer: nested_iter,
+        inner: None,
+    }
+}
+
+pub struct Concat<I>
+where
+    I: Iterator,
+    I::Item: Iterator,
+{
+    outer: I,
+    inner: Option<I::Item>,
+}
+
+impl<I> Iterator for Concat<I>
+where
+    I: Iterator,
+    I::Item: Iterator,
+{
+    type Item = <I::Item as Iterator>::Item;
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            if let Some(inner) = &mut self.inner {
+                if let Some(item) = inner.next() {
+                    return Some(item);
+                }
+            }
+            match self.outer.next() {
+                Some(next_inner) => self.inner = Some(next_inner),
+                None => return None,
+            }
+        }
+    }
+}
+
+/// Gibt einen Iterator über alle Elemente zurück, für die das Prädikat true ergibt (ohne filter)
+pub fn filter<I, F>(iter: I, predicate: F) -> Filter<I, F>
+where
+    I: Iterator,
+    F: Fn(&I::Item) -> bool,
+{
+    Filter { iter, predicate }
+}
+
+pub struct Filter<I, F> {
+    iter: I,
+    predicate: F,
+}
+
+impl<I, F> Iterator for Filter<I, F>
+where
+    I: Iterator,
+    F: Fn(&I::Item) -> bool,
+{
+    type Item = I::Item;
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(item) = self.iter.next() {
+            if (self.predicate)(&item) {
+                return Some(item);
+            }
+        }
+        None
+    }
+}
+
+pub fn length<I: Iterator>(mut iter: I) -> usize {
+    let mut n = 0;
+    while let Some(_) = iter.next() {
+        n += 1;
+    }
+    n
+}
+
+/// Gibt einen Iterator mit den Ergebnissen der Funktion auf alle Elemente zurück (ohne map)
+pub fn map<I, F, U>(iter: I, function: F) -> Map<I, F>
+where
+    I: Iterator,
+    F: Fn(I::Item) -> U,
+{
+    Map { iter, function }
+}
+
+pub struct Map<I, F> {
+    iter: I,
+    function: F,
+}
+
+impl<I, F, U> Iterator for Map<I, F>
+where
+    I: Iterator,
+    F: Fn(I::Item) -> U,
+{
+    type Item = U;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next().map(&self.function)
+    }
+}
+
+pub fn foldl<I, F, U>(mut iter: I, mut acc: U, function: F) -> U
+where
+    I: Iterator,
+    F: Fn(U, I::Item) -> U,
+{
+    while let Some(item) = iter.next() {
+        acc = function(acc, item);
+    }
+    acc
+}
+
+pub fn foldr<I, F, U>(mut iter: I, acc: U, function: F) -> U
+where
+    I: DoubleEndedIterator,
+    F: Fn(U, I::Item) -> U,
+{
+    // Sammle alle Elemente in einen Vektor, dann von rechts falten
+    let mut items = Vec::new();
+    while let Some(item) = iter.next() {
+        items.push(item);
+    }
+    let mut acc = acc;
+    while let Some(item) = items.pop() {
+        acc = function(acc, item);
+    }
+    acc
+}
+
+/// Gibt einen Iterator mit allen ursprünglichen Elementen in umgekehrter Reihenfolge zurück (ohne rev)
+pub fn reverse<I: DoubleEndedIterator>(iter: I) -> Reverse<I>
+where
+    I: DoubleEndedIterator,
+{
+    Reverse { iter, finished: false }
+}
+
+pub struct Reverse<I> {
+    iter: I,
+    finished: bool,
+}
+
+impl<I> Iterator for Reverse<I>
+where
+    I: DoubleEndedIterator,
+{
+    type Item = I::Item;
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.finished {
+            None
+        } else {
+            let next = self.iter.next_back();
+            if next.is_none() {
+                self.finished = true;
+            }
+            next
+        }
+    }
+}