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[pull] master from TheAlgorithms:master #215

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Merged
pull merged 1 commit into AlgorithmAndLeetCode:master from TheAlgorithms:master
Dec 5, 2025
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2 changes: 2 additions & 0 deletions src/data_structures/mod.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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;
Expand Down
377 changes: 377 additions & 0 deletions src/data_structures/skip_list.rs
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -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));
}
}
}

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