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/// Find all duplicate elements in a collection (elements that appear more than once).
/// Each duplicate element appears exactly once in the result.
///
/// # Arguments
/// * `collection` - A slice of items.
///
/// # Returns
/// * `Vec<T>` - A vector containing one instance of each duplicate element.
///
/// # Examples
/// ```rust
/// use lowdash::find_duplicates;
/// let numbers = vec![1, 2, 2, 3, 3, 4];
/// let result = find_duplicates(&numbers);
/// assert_eq!(result, vec![2, 3]);
/// ```
///
/// ```rust
/// use lowdash::find_duplicates;
/// let words = vec!["apple", "banana", "apple", "cherry", "banana"];
/// let result = find_duplicates(&words);
/// assert_eq!(result, vec!["apple", "banana"]);
/// ```
///
/// ```rust
/// use lowdash::find_duplicates;
///
/// #[derive(Debug, Clone, PartialEq, Eq, Hash)]
/// struct Person {
/// name: String,
/// age: u32,
/// }
///
/// let people = vec![
/// Person { name: "Alice".to_string(), age: 25 },
/// Person { name: "Bob".to_string(), age: 30 },
/// Person { name: "Alice".to_string(), age: 25 },
/// ];
///
/// let result = find_duplicates(&people);
/// assert_eq!(result, vec![Person { name: "Alice".to_string(), age: 25 }]);
/// ```
pub fn find_duplicates<T>(collection: &[T]) -> Vec<T>
where
T: Clone + Eq + std::hash::Hash,
{
use std::collections::HashMap;
let mut seen: HashMap<&T, bool> = HashMap::new();
let mut result = Vec::new();
// Track items and their duplicate status
for item in collection {
match seen.get(item) {
Some(&already_added) => {
if !already_added {
result.push(item.clone());
seen.insert(item, true);
}
}
None => {
seen.insert(item, false);
}
}
}
result
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_find_duplicates_numbers() {
let collection = vec![1, 2, 2, 3, 3, 4];
let result = find_duplicates(&collection);
assert_eq!(result, vec![2, 3]);
}
#[test]
fn test_find_duplicates_strings() {
let collection = vec!["apple", "banana", "apple", "cherry", "banana"];
let result = find_duplicates(&collection);
assert_eq!(result, vec!["apple", "banana"]);
}
#[test]
fn test_find_duplicates_empty() {
let collection: Vec<i32> = vec![];
let result = find_duplicates(&collection);
assert_eq!(result, Vec::<i32>::new());
}
#[test]
fn test_find_duplicates_no_duplicates() {
let collection = vec![1, 2, 3, 4, 5];
let result = find_duplicates(&collection);
assert_eq!(result, Vec::<i32>::new());
}
#[test]
fn test_find_duplicates_all_duplicates() {
let collection = vec![1, 1, 2, 2, 3, 3];
let result = find_duplicates(&collection);
assert_eq!(result, vec![1, 2, 3]);
}
#[test]
fn test_find_duplicates_multiple_occurrences() {
let collection = vec![1, 1, 1, 2, 2, 2];
let result = find_duplicates(&collection);
assert_eq!(result, vec![1, 2]);
}
#[test]
fn test_find_duplicates_with_struct() {
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct Person {
name: String,
age: u32,
}
let people = vec![
Person {
name: "Alice".to_string(),
age: 25,
},
Person {
name: "Bob".to_string(),
age: 30,
},
Person {
name: "Alice".to_string(),
age: 25,
},
Person {
name: "Bob".to_string(),
age: 30,
},
];
let result = find_duplicates(&people);
assert_eq!(
result,
vec![
Person {
name: "Alice".to_string(),
age: 25,
},
Person {
name: "Bob".to_string(),
age: 30,
},
]
);
}
}