Add rust mergeable heap

rust/Cargo.toml

@@ -4,6 +4,9 @@ version = "0.1.0"
 
 edition = "2021"
 
+[dependencies]
+rand = "0.8.5"
+
 [dev-dependencies]
 rstest="0.22.0"
 

rust/structures/mergeable_heap.rs

@@ -0,0 +1,75 @@
+use std::mem::swap;
+use std::rc::Rc;
+
+struct Heap<V> {
+    value: V,
+    left: Option<Rc<Heap<V>>>,
+    right: Option<Rc<Heap<V>>>,
+}
+
+impl<V: PartialOrd + Clone> Heap<V> {
+    fn new(value: V) -> Option<Rc<Heap<V>>> {
+        Some(Rc::new(Self {
+            value,
+            left: None,
+            right: None,
+        }))
+    }
+    fn merge(a: &Option<Rc<Heap<V>>>, b: &Option<Rc<Heap<V>>>) -> Option<Rc<Heap<V>>> {
+        if a.is_none() {
+            return b.clone();
+        }
+        if b.is_none() {
+            return a.clone();
+        }
+        let mut ra = a.clone()?;
+        let mut rb = b.clone()?;
+        if ra.value > rb.value {
+            swap(&mut ra, &mut rb);
+        }
+        if rand::random() {
+            ra = Rc::new(Heap {
+                value: ra.value.clone(),
+                left: ra.right.clone(),
+                right: ra.left.clone(),
+            });
+        }
+        Some(Rc::new(Heap {
+            value: ra.value.clone(),
+            left: Self::merge(&ra.left.clone(), &Some(rb)),
+            right: ra.right.clone(),
+        }))
+    }
+
+    fn remove_min(heap: &Option<Rc<Heap<V>>>) -> (Option<Rc<Heap<V>>>, V) {
+        let h = heap.as_ref().unwrap();
+        (
+            Self::merge(&h.as_ref().left, &h.as_ref().right),
+            h.as_ref().value.clone(),
+        )
+    }
+
+    fn add(heap: &Option<Rc<Heap<V>>>, value: V) -> Option<Rc<Heap<V>>> {
+        Self::merge(heap, &Heap::new(value))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::structures::mergeable_heap::Heap;
+
+    #[test]
+    fn basic_test() {
+        let mut h = None;
+        h = Heap::add(&h, 3);
+        h = Heap::add(&h, 1);
+        h = Heap::add(&h, 2);
+        let mut values = Vec::new();
+        while h.is_some() {
+            let (heap, min_value) = Heap::remove_min(&h);
+            values.push(min_value);
+            h = heap;
+        }
+        assert_eq!(values, [1, 2, 3]);
+    }
+}

rust/structures/mod.rs

@@ -1,3 +1,4 @@
 pub mod disjoint_sets;
 pub mod fenwick_tree;
+pub mod mergeable_heap;
 pub mod persistent_tree;