diff --git a/treap/README.mbt.md b/treap/README.mbt.md
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+++ b/treap/README.mbt.md
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+# Treap
+
+Randomized binary search tree for MoonBit. Each node stores a randomly assigned
+priority so the structure stays balanced in expectation, while still behaving
+like an ordered map keyed by `Compare` values.
+
+## Highlights
+- Generic in both key and value types; only requires `Compare` on keys.
+- Supports `insert`, `get`, `contains`, `remove`, `clear`, `len`, and `is_empty`.
+- Deterministic pseudo-random priorities keep the tree reproducible in tests.
+
+## Quick Start
+```moonbit
+test "README treap usage" {
+  let treap : Treap[Int, String] = Treap::new()
+  treap.insert(8, "eight")
+  treap.insert(3, "three")
+  treap.insert(5, "five")
+  assert_eq(treap.len(), 3)
+  assert_eq(treap.get(5), Some("five"))
+  assert_eq(treap.contains(7), false)
+
+  treap.insert(5, "FIVE")
+  assert_eq(treap.get(5), Some("FIVE"))
+  assert_eq(treap.remove(3), true)
+  assert_eq(treap.contains(3), false)
+
+  treap.clear()
+  assert_eq(treap.is_empty(), true)
+}
+```
+
+## API Overview
+- `Treap::new()` – construct an empty treap.
+- `insert(key, value)` – upsert a key/value pair.
+- `get(key)` – retrieve the stored value or `None`.
+- `contains(key)` – boolean membership query.
+- `remove(key)` – delete the entry if present.
+- `clear()` – empty the structure while retaining capacity.
+- `len()` / `is_empty()` – observe current occupancy.
+
+> ℹ️ The internal priority generator is deterministic, making results stable
+> across runs while still preserving the balancing guarantees of treaps.
diff --git a/treap/README.md b/treap/README.md
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+++ b/treap/README.md
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+README.mbt.md
\ No newline at end of file
diff --git a/treap/moon.pkg.json b/treap/moon.pkg.json
new file mode 100644
index 0000000..0967ef4
--- /dev/null
+++ b/treap/moon.pkg.json
@@ -0,0 +1 @@
+{}
diff --git a/treap/treap.mbt b/treap/treap.mbt
new file mode 100644
index 0000000..e00d9b2
--- /dev/null
+++ b/treap/treap.mbt
@@ -0,0 +1,226 @@
+///|
+struct Node[K, V] {
+  key : K
+  mut value : V
+  priority : Int
+  mut left : Node[K, V]?
+  mut right : Node[K, V]?
+}
+
+///|
+fn[K, V] Node::new(key : K, value : V, priority : Int) -> Node[K, V] {
+  Node::{ key, value, priority, left: None, right: None }
+}
+
+///|
+fn[K : Compare, V] split(
+  node_opt : Node[K, V]?,
+  key : K,
+) -> (Node[K, V]?, Node[K, V]?) {
+  match node_opt {
+    None => (None, None)
+    Some(node_value) => {
+      let node = node_value
+      if key.compare(node.key) < 0 {
+        let (less, greater) = split(node.left, key)
+        node.left = greater
+        (less, Some(node))
+      } else {
+        let (less, greater) = split(node.right, key)
+        node.right = less
+        (Some(node), greater)
+      }
+    }
+  }
+}
+
+///|
+fn[K : Compare, V] merge(
+  left_opt : Node[K, V]?,
+  right_opt : Node[K, V]?,
+) -> Node[K, V]? {
+  match (left_opt, right_opt) {
+    (None, right_side) => right_side
+    (left_side, None) => left_side
+    (Some(left_value), Some(right_value)) => {
+      let left = left_value
+      let right = right_value
+      if left.priority > right.priority {
+        let merged = merge(left.right, Some(right))
+        left.right = merged
+        Some(left)
+      } else {
+        let merged = merge(Some(left), right.left)
+        right.left = merged
+        Some(right)
+      }
+    }
+  }
+}
+
+///|
+fn[K : Compare, V] insert_node(
+  node_opt : Node[K, V]?,
+  key : K,
+  value : V,
+  priority : Int,
+) -> (Node[K, V]?, Bool) {
+  match node_opt {
+    None => (Some(Node::new(key, value, priority)), true)
+    Some(node_value) => {
+      let node = node_value
+      let cmp = key.compare(node.key)
+      if cmp == 0 {
+        node.value = value
+        (Some(node), false)
+      } else if priority > node.priority {
+        let (less, greater) = split(Some(node), key)
+        let new_node = Node::new(key, value, priority)
+        new_node.left = less
+        new_node.right = greater
+        (Some(new_node), true)
+      } else if cmp < 0 {
+        let (new_left, inserted) = insert_node(node.left, key, value, priority)
+        node.left = new_left
+        (Some(node), inserted)
+      } else {
+        let (new_right, inserted) = insert_node(
+          node.right,
+          key,
+          value,
+          priority,
+        )
+        node.right = new_right
+        (Some(node), inserted)
+      }
+    }
+  }
+}
+
+///|
+fn[K : Compare, V] remove_node(
+  node_opt : Node[K, V]?,
+  key : K,
+) -> (Node[K, V]?, Bool) {
+  match node_opt {
+    None => (None, false)
+    Some(node_value) => {
+      let node = node_value
+      let cmp = key.compare(node.key)
+      if cmp == 0 {
+        let merged = merge(node.left, node.right)
+        (merged, true)
+      } else if cmp < 0 {
+        let (new_left, removed) = remove_node(node.left, key)
+        node.left = new_left
+        (Some(node), removed)
+      } else {
+        let (new_right, removed) = remove_node(node.right, key)
+        node.right = new_right
+        (Some(node), removed)
+      }
+    }
+  }
+}
+
+///|
+fn[K : Compare, V] find_node(node_opt : Node[K, V]?, key : K) -> V? {
+  match node_opt {
+    None => None
+    Some(node_value) => {
+      let node = node_value
+      let cmp = key.compare(node.key)
+      if cmp == 0 {
+        Some(node.value)
+      } else if cmp < 0 {
+        find_node(node.left, key)
+      } else {
+        find_node(node.right, key)
+      }
+    }
+  }
+}
+
+///|
+pub struct Treap[K, V] {
+  mut root : Node[K, V]?
+  mut size : Int
+  mut rng_state : Int
+}
+
+///|
+pub fn[K, V] Treap::new() -> Treap[K, V] {
+  Treap::{ root: None, size: 0, rng_state: 123_456_789 }
+}
+
+///|
+pub fn[K, V] len(self : Treap[K, V]) -> Int {
+  self.size
+}
+
+///|
+pub fn[K, V] is_empty(self : Treap[K, V]) -> Bool {
+  self.size == 0
+}
+
+///|
+pub fn[K, V] clear(self : Treap[K, V]) -> Unit {
+  self.root = None
+  self.size = 0
+}
+
+///|
+fn[K, V] Treap::next_priority(self : Treap[K, V]) -> Int {
+  let modulus = 2_147_483_647
+  let mut state = (self.rng_state * 1_103_515_245 + 12_345) % modulus
+  if state < 0 {
+    state = -state
+  }
+  if state == 0 {
+    state = 1
+  }
+  self.rng_state = state
+  state
+}
+
+///|
+pub fn[K : Compare, V] Treap::insert(
+  self : Treap[K, V],
+  key : K,
+  value : V,
+) -> Unit {
+  let priority = self.next_priority()
+  let (new_root, inserted) = insert_node(self.root, key, value, priority)
+  self.root = new_root
+  if inserted {
+    self.size = self.size + 1
+  }
+}
+
+///|
+pub fn[K : Compare, V] Treap::get(self : Treap[K, V], key : K) -> V? {
+  find_node(self.root, key)
+}
+
+///|
+pub fn[K : Compare, V] Treap::contains(self : Treap[K, V], key : K) -> Bool {
+  match self.get(key) {
+    Some(_) => true
+    None => false
+  }
+}
+
+///|
+pub fn[K : Compare, V] Treap::remove(self : Treap[K, V], key : K) -> Bool {
+  let (new_root, removed) = remove_node(self.root, key)
+  self.root = new_root
+  if removed {
+    self.size = self.size - 1
+  }
+  removed
+}
+
+///|
+pub impl[K, V] Default for Treap[K, V] with default() {
+  Treap::new()
+}
diff --git a/treap/treap.mbti b/treap/treap.mbti
new file mode 100644
index 0000000..5f88092
--- /dev/null
+++ b/treap/treap.mbti
@@ -0,0 +1,29 @@
+// Generated using `moon info`, DON'T EDIT IT
+package "Lampese/Algorithms-Moonbit/treap"
+
+// Values
+
+// Errors
+
+// Types and methods
+type Node[K, V]
+
+pub struct Treap[K, V] {
+  mut root : Node[K, V]?
+  mut size : Int
+  mut rng_state : Int
+}
+fn[K, V] Treap::clear(Self[K, V]) -> Unit
+fn[K : Compare, V] Treap::contains(Self[K, V], K) -> Bool
+fn[K : Compare, V] Treap::get(Self[K, V], K) -> V?
+fn[K : Compare, V] Treap::insert(Self[K, V], K, V) -> Unit
+fn[K, V] Treap::is_empty(Self[K, V]) -> Bool
+fn[K, V] Treap::len(Self[K, V]) -> Int
+fn[K, V] Treap::new() -> Self[K, V]
+fn[K : Compare, V] Treap::remove(Self[K, V], K) -> Bool
+impl[K, V] Default for Treap[K, V]
+
+// Type aliases
+
+// Traits
+
diff --git a/treap/treap_test.mbt b/treap/treap_test.mbt
new file mode 100644
index 0000000..64b99ea
--- /dev/null
+++ b/treap/treap_test.mbt
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+///|
+test "treap basic operations" {
+  let treap : Treap[Int, Int] = Treap::new()
+  assert_eq(treap.is_empty(), true)
+  treap.insert(10, 100)
+  treap.insert(5, 50)
+  treap.insert(20, 200)
+  assert_eq(treap.len(), 3)
+  assert_eq(treap.is_empty(), false)
+  assert_eq(treap.get(10), Some(100))
+  assert_eq(treap.get(5), Some(50))
+  assert_eq(treap.get(20), Some(200))
+  assert_eq(treap.contains(15), false)
+}
+
+///|
+test "treap duplicate update preserves size" {
+  let treap : Treap[Int, String] = Treap::new()
+  treap.insert(1, "one")
+  treap.insert(2, "two")
+  treap.insert(3, "three")
+  assert_eq(treap.len(), 3)
+  treap.insert(2, "TWO")
+  assert_eq(treap.len(), 3)
+  assert_eq(treap.get(2), Some("TWO"))
+}
+
+///|
+test "treap removal cases" {
+  let treap : Treap[Int, Int] = Treap::new()
+  let values = [7, 3, 10, 1, 5, 9, 12]
+  for value in values {
+    treap.insert(value, value * 2)
+  }
+  assert_eq(treap.len(), values.length())
+  assert_eq(treap.remove(3), true)
+  assert_eq(treap.contains(3), false)
+  assert_eq(treap.remove(10), true)
+  assert_eq(treap.contains(10), false)
+  assert_eq(treap.remove(8), false)
+  assert_eq(treap.len(), values.length() - 2)
+  assert_eq(treap.get(9), Some(18))
+  assert_eq(treap.get(12), Some(24))
+}
+
+///|
+test "treap clear resets structure" {
+  let treap : Treap[Int, Int] = Treap::default()
+  for value in [1, 2, 3, 4, 5] {
+    treap.insert(value, value)
+  }
+  assert_eq(treap.len(), 5)
+  treap.clear()
+  assert_eq(treap.len(), 0)
+  assert_eq(treap.is_empty(), true)
+  assert_eq(treap.get(3), None)
+  assert_eq(treap.remove(3), false)
+}
+
+///|
+test "treap handles larger sequence" {
+  let treap : Treap[Int, Int] = Treap::new()
+  for value in 0..<100 {
+    treap.insert(value, value)
+  }
+  assert_eq(treap.len(), 100)
+  for value in 0..<100 {
+    assert_eq(treap.get(value), Some(value))
+  }
+  for value in 0..<50 {
+    assert_eq(treap.remove(value), true)
+  }
+  assert_eq(treap.len(), 50)
+  for value in 0..<50 {
+    assert_eq(treap.contains(value), false)
+  }
+  for value in 50..<100 {
+    assert_eq(treap.contains(value), true)
+  }
+}