diff --git a/README.md b/README.md
index fb2e4e8..14d19f1 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ The `ladderz` project is a collection of math and tech concepts implemented in c
 
 -   **[`ladderz` library](https://rzmk.github.io/ladderz/)** - A Rust library for running concept implementations
 -   **[`lz` CLI](lz)** - A command line tool for running ladderz functions
--   **[notebooks](notebooks)** - Jupyter notebooks with concept exercises and solutions in Python
+-   **[notebooks](notebooks)** - Rust & Python Jupyter notebooks with concept exercises and solutions
 
 > If you're looking for a more efficient implementation of a concept (e.g., for use in your programs), other resources may be more useful.
 
@@ -41,7 +41,7 @@ Now let's run the `lz` CLI tool with the `prealgebra` subject and `get-factors`
 lz prealgebra get-factors 12
 ```
 
-The printed output should be:
+The printed output may be:
 
 ```console
 The factors of 12 are {2, 3, 6, 1, 4, 12}.
@@ -53,7 +53,7 @@ We can use the `--raw` flag to get the raw output of the function:
 lz prealgebra get-factors 12 --raw
 ```
 
-The printed output may be:
+The printed raw output may be:
 
 ```console
 {1, 2, 3, 4, 6, 12}
@@ -154,7 +154,6 @@ Not currently implemented, but ideas that may be useful:
     -   Linear Algebra
     -   Statistics
     -   Discrete Math
-    -   Algorithms
     -   Bioinformatics
 -   **ladderz-py** - A package for running implementations of mathematical concepts in Python
 -   **ladderz-app** - An interactive cross-platform (web, desktop, mobile) app potentially including visualizations, practice problems, & a course-like structure (potentially in Flutter or Tauri with Next.js & Rust)
diff --git a/ladderz/src/dsa.rs b/ladderz/src/dsa.rs
new file mode 100644
index 0000000..fd8c576
--- /dev/null
+++ b/ladderz/src/dsa.rs
@@ -0,0 +1,24 @@
+use std::collections::HashSet;
+
+pub fn contains_duplicate(nums: Vec<i32>) -> bool {
+    let mut seen = HashSet::<i32>::new();
+    for &num in nums.iter() {
+        if seen.contains(&num) {
+            return true;
+        }
+        seen.insert(num);
+    }
+    false
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_contains_duplicate() {
+        let result = contains_duplicate(vec![1, 2, 3, 2]);
+        let expected = true;
+        assert_eq!(result, expected);
+    }
+}
diff --git a/ladderz/src/lib.rs b/ladderz/src/lib.rs
index c29077c..d27c49c 100644
--- a/ladderz/src/lib.rs
+++ b/ladderz/src/lib.rs
@@ -9,7 +9,7 @@
 //! ```toml
 //! ladderz = { git = "https://github.com/rzmk/ladderz", branch = "main" }
 //! ```
-//! 
+//!
 //! # Example
 //!
 //! ```rust
@@ -43,3 +43,21 @@
 /// ```
 ///
 pub mod prealgebra;
+
+/// Various data structures and algorithms implementations.
+///
+/// # Example
+///
+/// ```rust
+/// use ladderz::dsa::contains_duplicate;
+///
+/// let nums: Vec<i32> = vec![2, 3, 4, 2];
+/// let result = contains_duplicate(nums.clone());
+/// println!("The vector {:?} {} contain a duplicate.", &nums, if result { "does" } else { "does not" });
+/// ```
+///
+/// ```console
+/// The vector [2, 3, 4, 2] does contain a duplicate.
+/// ```
+///
+pub mod dsa;
diff --git a/ladderz/src/prealgebra.rs b/ladderz/src/prealgebra.rs
index ab110f0..d26cc8b 100644
--- a/ladderz/src/prealgebra.rs
+++ b/ladderz/src/prealgebra.rs
@@ -113,7 +113,7 @@ pub fn is_multiple(x: u32, y: u32) -> bool {
     x % y == 0
 }
 
-/// Finds all the multiples of a positive integer `n` up to and including `end` (in the range [n, end]).
+/// Finds all the multiples of a positive integer `n` starting from `start` and ending at `end` (inclusive).
 ///
 /// A multiple of `n` is a positive integer `num` where `num` is evenly divisible by `n` (i.e., `num % n == 0`).
 ///
@@ -123,14 +123,18 @@ pub fn is_multiple(x: u32, y: u32) -> bool {
 /// use ladderz::prealgebra::get_multiples_in_range;
 /// use std::collections::HashSet;
 ///
-/// let result: HashSet<u32> = get_multiples_in_range(2, 10);
-/// let expected: HashSet<u32> = [2, 4, 6, 8, 10].into();
+/// let result: HashSet<u32> = get_multiples_in_range(2, 5, 10);
+/// let expected: HashSet<u32> = [6, 8, 10].into();
 /// assert_eq!(result, expected);
 /// ```
-pub fn get_multiples_in_range(n: u32, end: u32) -> HashSet<u32> {
+pub fn get_multiples_in_range(n: u32, start: u32, end: u32) -> HashSet<u32> {
     let mut multiples: HashSet<u32> = HashSet::new();
-
-    for num in (n..end + 1).step_by(n as usize) {
+    let initial = if start % n == 0 {
+        start
+    } else {
+        start + n - (start % n)
+    };
+    for num in (initial..end + 1).step_by(n as usize) {
         multiples.insert(num);
     }
     multiples
@@ -304,16 +308,16 @@ mod tests {
 
     #[test]
     fn test_get_multiples_in_range() {
-        let result: HashSet<u32> = get_multiples_in_range(2, 20);
-        let expected: HashSet<u32> = [2, 4, 6, 8, 10, 12, 14, 16, 18, 20].into();
+        let result: HashSet<u32> = get_multiples_in_range(2, 10, 20);
+        let expected: HashSet<u32> = [10, 12, 14, 16, 18, 20].into();
         assert_eq!(result, expected);
 
-        let result_2: HashSet<u32> = get_multiples_in_range(5, 34);
-        let expected_2: HashSet<u32> = [5, 10, 15, 20, 25, 30].into();
+        let result_2: HashSet<u32> = get_multiples_in_range(5, 23, 34);
+        let expected_2: HashSet<u32> = [25, 30].into();
         assert_eq!(result_2, expected_2);
 
-        let result_3: HashSet<u32> = get_multiples_in_range(7, 11);
-        let expected_3: HashSet<u32> = [7].into();
+        let result_3: HashSet<u32> = get_multiples_in_range(7, 10, 11);
+        let expected_3: HashSet<u32> = [].into();
         assert_eq!(expected_3, result_3);
     }
 
diff --git a/lz/src/dsa.rs b/lz/src/dsa.rs
new file mode 100644
index 0000000..60856b4
--- /dev/null
+++ b/lz/src/dsa.rs
@@ -0,0 +1,57 @@
+use clap::Subcommand;
+
+#[derive(Subcommand)]
+#[command(arg_required_else_help(true))]
+pub enum Dsa {
+    /// Returns true or false based on whether the vector has a duplicate.
+    ///
+    /// ## Example
+    ///
+    /// ### Input
+    ///
+    /// ```bash
+    /// lz dsa contains-duplicate 1,2,3,2
+    /// # Alternatively you may delimit the numbers with spaces:
+    /// lz dsa contains-duplicate 1 2 3 2
+    /// ```
+    ///
+    /// ### Output
+    ///
+    /// ```bash
+    /// The vector [1, 2, 3, 2] does contain a duplicate.
+    /// ```
+    ///
+    /// ## Raw Output (use `-r` or `--raw`)
+    ///
+    /// ```bash
+    /// true
+    /// ```
+    ContainsDuplicate {
+        /// The vector of numbers to detect whether it has a duplicate.
+        #[arg(value_delimiter = ',', num_args = 1)]
+        n: Vec<i32>,
+        /// Whether or not to return the raw output.
+        #[arg(short = 'r', long)]
+        raw: bool,
+    },
+}
+
+pub fn match_dsa(function: Option<Dsa>) {
+    use ladderz::dsa::*;
+    match function {
+        Some(Dsa::ContainsDuplicate { n, raw }) => match raw {
+            true => println!("{:?}", contains_duplicate(n)),
+            false => {
+                let result = contains_duplicate(n.clone());
+                println!(
+                    "The vector {:?} {} contain a duplicate.",
+                    &n,
+                    if result { "does" } else { "does not" }
+                )
+            }
+        },
+        None => {
+            println!("Please provide a function to use.");
+        }
+    }
+}
diff --git a/lz/src/main.rs b/lz/src/main.rs
index 46027d4..c9d4cb5 100644
--- a/lz/src/main.rs
+++ b/lz/src/main.rs
@@ -1,31 +1,31 @@
 //! # lz
-//! 
+//!
 //! A command-line interface for various math/tech subjects. Based on the [ladderz](https://github.com/rzmk/ladderz) library.
-//! 
+//!
 //! # Installation
-//! 
+//!
 //! To install the command-line interface, run the following command in your terminal:
-//! 
+//!
 //! ```bash
 //! cargo install --git https://github.com/rzmk/ladderz --branch main
 //! ```
-//! 
+//!
 //! # Example
-//! 
+//!
 //! ```bash
 //! lz prealgebra is-factor 3 12
 //! ```
-//! 
+//!
 //! ```console
 //! 3 is a factor of 12.
 //! ```
-//! 
+//!
 //! You may view the help menu for a subject and a function by running the command with the `-h` or `--help` flag:
-//! 
+//!
 //! ```bash
 //! lz prealgebra is-factor -h
 //! ```
-//! 
+//!
 //! Learn more on [GitHub](https://github.com/rzmk/ladderz).
 
 // External modules
@@ -34,6 +34,8 @@ use clap::{Parser, Subcommand};
 // Local modules
 pub mod prealgebra;
 use prealgebra::{match_prealgebra, Prealgebra};
+pub mod dsa;
+use dsa::{match_dsa, Dsa};
 
 #[derive(Parser)]
 #[command(
@@ -56,6 +58,10 @@ enum Subjects {
         #[command(subcommand)]
         function: Option<Prealgebra>,
     },
+    Dsa {
+        #[command(subcommand)]
+        function: Option<Dsa>,
+    },
 }
 
 fn main() {
@@ -64,8 +70,7 @@ fn main() {
     // Match the subject to run the correct function.
     match cli.subject {
         Some(Subjects::Prealgebra { function }) => match_prealgebra(function),
-        None => {
-            println!("Please provide a subject to use.");
-        }
+        Some(Subjects::Dsa { function }) => match_dsa(function),
+        None => println!("Please provide a subject to use."),
     }
 }
diff --git a/lz/src/prealgebra.rs b/lz/src/prealgebra.rs
index 5660ce2..c36c603 100644
--- a/lz/src/prealgebra.rs
+++ b/lz/src/prealgebra.rs
@@ -4,23 +4,23 @@ use clap::Subcommand;
 #[command(arg_required_else_help(true))]
 pub enum Prealgebra {
     /// Finds all factor pairs for a positive integer.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra factor-pairs 12
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// The factor pairs of 12 are {(1, 12), (2, 6), (3, 4)}.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// {(1, 12), (2, 6), (3, 4)}
     /// ```
@@ -34,21 +34,21 @@ pub enum Prealgebra {
     /// Finds all factors for a positive integer.
     ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra factors 12
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// The factors of 12 are {1, 2, 3, 4, 6, 12}.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// {1, 2, 3, 4, 6, 12}
     /// ```
@@ -60,29 +60,31 @@ pub enum Prealgebra {
         raw: bool,
     },
     /// Finds all multiples of a positive integer in a given range.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra multiples-in-range 3 10
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// The multiples of 3 in the range [1, 10] are {3, 6, 9}.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// {3, 6, 9}
     /// ```
     MultiplesInRange {
         /// The positive integer to find multiples for.
         n: u32,
+        /// The lower bound of the range to find multiples in.
+        lower_bound: u32,
         /// The upper bound of the range to find multiples in.
         upper_bound: u32,
         /// Whether or not to return the raw output.
@@ -90,23 +92,23 @@ pub enum Prealgebra {
         raw: bool,
     },
     /// Finds all primes in a given range.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra primes-in-range 1 10
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// The primes in the range [1, 10] are {2, 3, 7, 5}.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// {2, 3, 7, 5}
     /// ```
@@ -120,23 +122,23 @@ pub enum Prealgebra {
         raw: bool,
     },
     /// Finds the prime factorization of a positive integer.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra prime-factorization 12
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// The prime factorization of 12 is {3: 1, 2: 2}.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// {3: 1, 2: 2}
     /// ```
@@ -148,23 +150,23 @@ pub enum Prealgebra {
         raw: bool,
     },
     /// Determines if a positive integer is composite.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra is-composite 12
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// 12 is composite.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// true
     /// ```
@@ -176,23 +178,23 @@ pub enum Prealgebra {
         raw: bool,
     },
     /// Determines if a positive integer is prime.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra is-prime 12
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// 12 is not prime.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// false
     /// ```
@@ -204,23 +206,23 @@ pub enum Prealgebra {
         raw: bool,
     },
     /// Determines if a positive integer is a factor of another positive integer.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra is-factor 3 12
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// 3 is a factor of 12.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// true
     /// ```
@@ -234,23 +236,23 @@ pub enum Prealgebra {
         raw: bool,
     },
     /// Determines if a positive integer is a multiple of another positive integer.
-    /// 
+    ///
     /// ## Example
-    /// 
+    ///
     /// ### Input
-    /// 
+    ///
     /// ```bash
     /// lz prealgebra is-multiple 12 3
     /// ```
-    /// 
+    ///
     /// ### Output
-    /// 
+    ///
     /// ```bash
     /// 12 is a multiple of 3.
     /// ```
-    /// 
+    ///
     /// ## Raw Output (use `-r` or `--raw`)
-    /// 
+    ///
     /// ```bash
     /// true
     /// ```
@@ -278,15 +280,17 @@ pub fn match_prealgebra(function: Option<Prealgebra>) {
         },
         Some(Prealgebra::MultiplesInRange {
             n,
+            lower_bound,
             upper_bound,
             raw,
         }) => match raw {
-            true => println!("{:?}", get_multiples_in_range(n, upper_bound)),
+            true => println!("{:?}", get_multiples_in_range(n, lower_bound, upper_bound)),
             false => println!(
-                "The multiples of {} in the range [1, {}] are {:?}.",
+                "The multiples of {} in the range [{}, {}] are {:?}.",
                 n,
+                lower_bound,
                 upper_bound,
-                get_multiples_in_range(n, upper_bound)
+                get_multiples_in_range(n, lower_bound, upper_bound)
             ),
         },
         Some(Prealgebra::PrimesInRange {
@@ -340,8 +344,6 @@ pub fn match_prealgebra(function: Option<Prealgebra>) {
                 m
             ),
         },
-        None => {
-            println!("Please provide a function to use.");
-        }
+        None => println!("Please provide a function to use."),
     }
 }
diff --git a/notebooks/pre-algebra.ipynb b/notebooks/python/pre-algebra.ipynb
similarity index 100%
rename from notebooks/pre-algebra.ipynb
rename to notebooks/python/pre-algebra.ipynb
diff --git a/notebooks/requirements.txt b/notebooks/python/requirements.txt
similarity index 100%
rename from notebooks/requirements.txt
rename to notebooks/python/requirements.txt
diff --git a/notebooks/rust/dsa.ipynb b/notebooks/rust/dsa.ipynb
new file mode 100644
index 0000000..3e136db
--- /dev/null
+++ b/notebooks/rust/dsa.ipynb
@@ -0,0 +1,80 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# ladderz dsa usage\n",
+    "\n",
+    "Here are some examples of using the `dsa` (data structures and algorithms) module from `ladderz`.\n",
+    "\n",
+    "> This notebook uses [evcxr](https://github.com/evcxr/evcxr) for a Rust Jupyter Kernel. See [the evcxr_jupyter README.md](https://github.com/evcxr/evcxr/blob/main/evcxr_jupyter/README.md) for more info on how to run this notebook on your machine."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "vscode": {
+     "languageId": "rust"
+    }
+   },
+   "outputs": [],
+   "source": [
+    "// Uncomment the next line and comment the subsequent line if not running notebook from source\n",
+    "// :dep ladderz = { git = \"https://github.com/rzmk/ladderz\", branch = \"main\" }\n",
+    ":dep ladderz = { path = \"../../ladderz\" }\n",
+    "\n",
+    "use ladderz::dsa;"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## 217. Contains Duplicate"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "metadata": {
+    "vscode": {
+     "languageId": "rust"
+    }
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "true"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "dsa::contains_duplicate(vec![1, 3, 4, 2, 4])"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Rust",
+   "language": "rust",
+   "name": "rust"
+  },
+  "language_info": {
+   "codemirror_mode": "rust",
+   "file_extension": ".rs",
+   "mimetype": "text/rust",
+   "name": "Rust",
+   "pygment_lexer": "rust",
+   "version": ""
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}