Add skip list (#954)

Author: zhangzhuang15

src/data_structures/mod.rs

@@ -14,6 +14,7 @@ mod range_minimum_query;
 mod rb_tree;
 mod segment_tree;
 mod segment_tree_recursive;
+mod skip_list;
 mod stack_using_singly_linked_list;
 mod treap;
 mod trie;
@@ -38,6 +39,7 @@ pub use self::range_minimum_query::RangeMinimumQuery;
 pub use self::rb_tree::RBTree;
 pub use self::segment_tree::SegmentTree;
 pub use self::segment_tree_recursive::SegmentTree as SegmentTreeRecursive;
+pub use self::skip_list::SkipList;
 pub use self::stack_using_singly_linked_list::Stack;
 pub use self::treap::Treap;
 pub use self::trie::Trie;

src/data_structures/skip_list.rs

@@ -0,0 +1,377 @@
+use rand::random_range;
+use std::{cmp::Ordering, marker::PhantomData, ptr::null_mut};
+
+struct Node<K: Ord, V> {
+    key: Option<K>,
+    value: Option<V>,
+    forward: Vec<*mut Node<K, V>>,
+}
+
+impl<K: Ord, V> Node<K, V> {
+    pub fn new() -> Self {
+        let mut forward = Vec::with_capacity(4);
+        forward.resize(4, null_mut());
+        Node {
+            key: None,
+            value: None,
+            forward,
+        }
+    }
+
+    pub fn make_node(capacity: usize, key: K, value: V) -> Self {
+        let mut new_node = Self::new();
+        new_node.key = Some(key);
+        new_node.value = Some(value);
+        new_node.forward = Vec::<*mut Node<K, V>>::with_capacity(capacity);
+        new_node.forward.resize(capacity, null_mut());
+        new_node
+    }
+}
+
+/// A probabilistic data structure that maintains a sorted collection of key-value pairs.
+///
+/// A skip list is a data structure that allows O(log n) search, insertion, and deletion
+/// on average by maintaining multiple levels of linked lists with probabilistic balancing.
+pub struct SkipList<K: Ord, V> {
+    header: *mut Node<K, V>,
+    level: usize,
+    max_level: usize,
+    marker: PhantomData<Node<K, V>>,
+}
+
+impl<K: Ord, V> SkipList<K, V> {
+    pub fn new(max_level: usize) -> Self {
+        let mut node = Box::new(Node::<K, V>::new());
+        node.forward = Vec::with_capacity(max_level);
+        node.forward.resize(max_level, null_mut());
+
+        SkipList {
+            header: Box::into_raw(node),
+            level: 0,
+            max_level,
+            marker: PhantomData,
+        }
+    }
+
+    pub fn search(&self, searched_key: K) -> Option<&V> {
+        let mut x = self.header;
+
+        unsafe {
+            'outer: for i in (0..self.level).rev() {
+                loop {
+                    let forward_i = (&*x).forward[i];
+                    if forward_i.is_null() {
+                        continue 'outer;
+                    }
+
+                    let forward_i_key = (*forward_i).key.as_ref();
+                    match forward_i_key.cmp(&Some(&searched_key)) {
+                        Ordering::Less => {
+                            x = forward_i;
+                        }
+                        _ => {
+                            break;
+                        }
+                    }
+                }
+            }
+
+            x = (&*x).forward[0];
+            if x.is_null() {
+                return None;
+            }
+
+            match (*x).key.as_ref().cmp(&Some(&searched_key)) {
+                Ordering::Equal => {
+                    return (*x).value.as_ref();
+                }
+                _ => {
+                    return None;
+                }
+            }
+        }
+    }
+
+    pub fn insert(&mut self, searched_key: K, new_value: V) -> bool {
+        let mut update = Vec::<*mut Node<K, V>>::with_capacity(self.max_level);
+        update.resize(self.max_level, null_mut());
+
+        let mut x = self.header;
+
+        unsafe {
+            for i in (0..self.level).rev() {
+                loop {
+                    let x_forward_i = (&*x).forward[i];
+                    if x_forward_i.is_null() {
+                        break;
+                    }
+
+                    let x_forward_i_key = (*x_forward_i).key.as_ref();
+                    match x_forward_i_key.cmp(&Some(&searched_key)) {
+                        Ordering::Less => {
+                            x = x_forward_i;
+                        }
+                        _ => {
+                            break;
+                        }
+                    }
+                }
+                let update_i = &mut update[i];
+                *update_i = x;
+            }
+
+            let x_forward_i = (&*x).forward[0];
+            x = x_forward_i;
+            if x.is_null() || (*x).key.as_ref().cmp(&Some(&searched_key)) != Ordering::Equal {
+                let v = random_value(self.max_level);
+                if v > self.level {
+                    for update_i in update.iter_mut().take(v).skip(self.level) {
+                        *update_i = self.header;
+                    }
+                    self.level = v;
+                }
+                let new_node = Node::make_node(v, searched_key, new_value);
+                x = Box::into_raw(Box::new(new_node));
+
+                for (i, t) in update.iter_mut().enumerate().take(self.level) {
+                    let x_forward_i = (&mut *x).forward.get_mut(i);
+                    if x_forward_i.is_none() {
+                        break;
+                    }
+                    let x_forward_i = x_forward_i.unwrap();
+                    let update_i = t;
+                    let update_i_forward_i = &mut (&mut **update_i).forward[i];
+                    *x_forward_i = *update_i_forward_i;
+                    *update_i_forward_i = x;
+                }
+                return true;
+            }
+            (*x).value.replace(new_value);
+            return true;
+        }
+    }
+
+    pub fn delete(&mut self, searched_key: K) -> bool {
+        let mut update = Vec::<*mut Node<K, V>>::with_capacity(self.max_level);
+        update.resize(self.max_level, null_mut());
+
+        let mut x = self.header;
+
+        unsafe {
+            for i in (0..self.level).rev() {
+                loop {
+                    let x_forward_i = (&*x).forward[i];
+                    if x_forward_i.is_null() {
+                        break;
+                    }
+
+                    let x_forward_i_key = (*x_forward_i).key.as_ref();
+                    match x_forward_i_key.cmp(&Some(&searched_key)) {
+                        Ordering::Less => {
+                            x = x_forward_i;
+                        }
+                        _ => {
+                            break;
+                        }
+                    }
+                }
+                let update_i = &mut update[i];
+                *update_i = x;
+            }
+
+            let x_forward_i = *((&*x).forward.first().unwrap());
+            x = x_forward_i;
+
+            if x.is_null() {
+                return false;
+            }
+
+            match (*x).key.as_ref().cmp(&Some(&searched_key)) {
+                Ordering::Equal => {
+                    for (i, update_i) in update.iter_mut().enumerate().take(self.level) {
+                        let update_i_forward_i = &mut (&mut **update_i).forward[i];
+                        if update_i_forward_i.is_null() {
+                            break;
+                        }
+
+                        let x_forward_i = (&mut *x).forward.get_mut(i);
+                        if x_forward_i.is_none() {
+                            break;
+                        }
+                        let x_forward_i = x_forward_i.unwrap();
+                        *update_i_forward_i = *x_forward_i;
+                    }
+
+                    let _v = Box::from_raw(x);
+
+                    loop {
+                        if self.level == 0 {
+                            break;
+                        }
+
+                        let header_forward_level = &(&*self.header).forward[self.level - 1];
+                        if header_forward_level.is_null() {
+                            self.level -= 1;
+                        } else {
+                            break;
+                        }
+                    }
+                    return true;
+                }
+                _ => {
+                    return false;
+                }
+            }
+        }
+    }
+
+    pub fn iter(&self) -> Iter<'_, K, V> {
+        Iter::new(self)
+    }
+}
+
+impl<K: Ord, V> Drop for SkipList<K, V> {
+    fn drop(&mut self) {
+        let mut node = unsafe { Box::from_raw(self.header) };
+        loop {
+            let node_forward_0 = node.forward.first().unwrap();
+            if node_forward_0.is_null() {
+                break;
+            }
+            node = unsafe { Box::from_raw(*node_forward_0) };
+        }
+    }
+}
+
+fn random_value(max: usize) -> usize {
+    let mut v = 1usize;
+    loop {
+        if random_range(1usize..10usize) > 5 && v < max {
+            v += 1;
+        } else {
+            break;
+        }
+    }
+    v
+}
+
+pub struct Iter<'a, K: Ord, V> {
+    current_node: *mut Node<K, V>,
+    _marker: PhantomData<&'a SkipList<K, V>>,
+}
+
+impl<'a, K: Ord, V> Iter<'a, K, V> {
+    pub fn new(skip_list: &'a SkipList<K, V>) -> Self {
+        Iter {
+            current_node: skip_list.header,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, K: Ord, V> Iterator for Iter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        unsafe {
+            let forward_0 = (&*self.current_node).forward.first();
+            forward_0?;
+            let forward_0 = *forward_0.unwrap();
+            if forward_0.is_null() {
+                return None;
+            }
+            self.current_node = forward_0;
+            return match ((*forward_0).key.as_ref(), (*forward_0).value.as_ref()) {
+                (Some(key), Some(value)) => Some((key, value)),
+                _ => None,
+            };
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    #[test]
+    fn insert_and_delete() {
+        let mut skip_list = super::SkipList::<&'static str, i32>::new(8);
+        skip_list.insert("a", 10);
+        skip_list.insert("b", 12);
+
+        {
+            let result = skip_list.search("b");
+            assert!(result.is_some());
+            assert_eq!(result, Some(&12));
+        }
+
+        {
+            skip_list.delete("b");
+            let result = skip_list.search("b");
+            assert!(result.is_none());
+        }
+
+        skip_list.delete("a");
+    }
+
+    #[test]
+    fn iterator() {
+        let mut skip_list = super::SkipList::<&'static str, i32>::new(8);
+        skip_list.insert("h", 22);
+        skip_list.insert("a", 12);
+        skip_list.insert("c", 11);
+
+        let result: Vec<(&&'static str, &i32)> = skip_list.iter().collect();
+        assert_eq!(result, vec![(&"a", &12), (&"c", &11), (&"h", &22)]);
+    }
+
+    #[test]
+    fn cannot_search() {
+        let mut skip_list = super::SkipList::<&'static str, i32>::new(8);
+
+        {
+            let result = skip_list.search("h");
+            assert!(result.is_none());
+        }
+
+        skip_list.insert("h", 10);
+
+        {
+            let result = skip_list.search("a");
+            assert!(result.is_none());
+        }
+    }
+
+    #[test]
+    fn delete_unsuccessfully() {
+        let mut skip_list = super::SkipList::<&'static str, i32>::new(8);
+
+        {
+            let result = skip_list.delete("a");
+            assert!(!result);
+        }
+
+        skip_list.insert("a", 10);
+
+        {
+            let result = skip_list.delete("b");
+            assert!(!result);
+        }
+    }
+
+    #[test]
+    fn update_value_with_insert_operation() {
+        let mut skip_list = super::SkipList::<&'static str, i32>::new(8);
+        skip_list.insert("a", 10);
+
+        {
+            let result = skip_list.search("a");
+            assert_eq!(result, Some(&10));
+        }
+
+        skip_list.insert("a", 100);
+
+        {
+            let result = skip_list.search("a");
+            assert_eq!(result, Some(&100));
+        }
+    }
+}