{"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"Which method allows adding an element to the end of a Vec?","acceptedAnswer":{"@type":"Answer","text":"The push() method adds an element to the end of the vector, increasing its size by 1. This operation has amortized O(1) complexity because the vector may need to reallocate memory if capacity is exceeded. To add multiple elements, extend() or append() can be used depending on the needs."}},{"@type":"Question","name":"What is the main difference between String and &str in Rust?","acceptedAnswer":{"@type":"Answer","text":"String is an owned type stored on the heap, mutable and resizable. &str is an immutable reference to a UTF-8 sequence, often called a 'string slice'. String owns its data and can be modified, while &str borrows existing data without owning it. This distinction is fundamental for memory management in Rust."}},{"@type":"Question","name":"How to create a new empty Vec in Rust?","acceptedAnswer":{"@type":"Answer","text":"Vec::new() creates an empty vector without initial allocation. The vec![] macro can also create an empty vector, but Vec::new() is the standard explicit method. The generic type can be inferred or explicitly specified with turbofish syntax Vec::::new() or by type annotation."}},{"@type":"Question","name":"What does the get() method return on a Vec?","acceptedAnswer":{"@type":"Answer","text":"The get() method returns Option<&T>, allowing safe access without panic. It returns Some(&element) if the index is valid, None otherwise. Unlike direct indexing with [], get() does not panic if the index is out of bounds. This is the recommended method when the index may be invalid."}},{"@type":"Question","name":"Which data structure to use for associating keys with values with O(1) average access?","acceptedAnswer":{"@type":"Answer","text":"HashMap offers O(1) average access through a hash table. Keys must implement the Eq and Hash traits. HashMap uses SipHash by default for HashDoS attack resistance. For ordered keys, BTreeMap offers an alternative with O(log n) access but maintains order."}},{"@type":"Question","name":"What is the difference between HashSet and HashMap in Rust?","acceptedAnswer":{"@type":"Answer","text":"HashSet stores only unique values without key-value associations, while HashMap associates keys with values. HashSet is optimized for checking element membership with contains(). Internally, HashSet is implemented as HashMap with empty values."}},{"@type":"Question","name":"What does the collect() method do on an iterator?","acceptedAnswer":{"@type":"Answer","text":"collect() consumes the iterator and gathers its elements into a collection. The target collection type must implement FromIterator. The return type is often inferred from context, otherwise turbofish syntax .collect::>() allows specifying it. This is a very powerful method for transforming iterators into collections."}},{"@type":"Question","name":"How to convert a &str to String in Rust?","acceptedAnswer":{"@type":"Answer","text":"Several methods exist: to_string(), String::from(), and to_owned(). to_string() is available via the ToString trait (implemented via Display). String::from() is explicit and idiomatic. to_owned() converts borrowed types to owned types. All three methods produce the same result for &str."}},{"@type":"Question","name":"What happens when iterating over a Vec with for item in vec?","acceptedAnswer":{"@type":"Answer","text":"Iteration with for item in vec consumes the vector (move). After the loop, the vector is no longer usable because ownership was transferred. To borrow without consuming, use for item in &vec (immutable references) or for item in &mut vec (mutable references). This distinction is crucial for ownership management."}},{"@type":"Question","name":"How to insert or update a value in a HashMap only if the key doesn't exist?","acceptedAnswer":{"@type":"Answer","text":"The entry() method combined with or_insert() allows inserting a value only if the key is absent. entry() returns an Entry enum that can be Occupied or Vacant. or_insert() inserts the value if Vacant and returns a mutable reference. or_insert_with() accepts a closure for lazy initialization."}},{"@type":"Question","name":"Which method to use to get the length of a Vec or String?","acceptedAnswer":{"@type":"Answer","text":"The len() method returns the number of elements for Vec and the number of bytes for String. For String, len() counts UTF-8 bytes, not characters. To count Unicode characters, use chars().count(). is_empty() allows checking if the collection is empty without computing the full length."}},{"@type":"Question","name":"Which trait must HashMap keys implement?","acceptedAnswer":{"@type":"Answer","text":"Keys must implement Eq (structural equality) and Hash (hashing). Eq allows comparing keys for equality, while Hash generates a hash value to locate entries. Primitive types and String implement these traits. Floating-point types (f32, f64) do not implement them because NaN != NaN."}},{"@type":"Question","name":"How to create a vector with initial values?","acceptedAnswer":{"@type":"Answer","text":"The vec![] macro allows creating a vector with initial values concisely. For example vec![1, 2, 3] creates a Vec with three elements. vec![0; 5] creates a vector of 5 zeros. This macro is more ergonomic than creating an empty vector then calling push() multiple times."}},{"@type":"Question","name":"How to iterate over key-value pairs of a HashMap?","acceptedAnswer":{"@type":"Answer","text":"Iterating over a HashMap with for (key, value) in &map gives references to key-value pairs. Without the &, the HashMap would be consumed. iter() is equivalent to &map. keys() and values() allow iterating only over keys or values. iter_mut() allows modifying values during iteration."}},{"@type":"Question","name":"What does the pop() method do on a Vec?","acceptedAnswer":{"@type":"Answer","text":"pop() removes and returns the last element of the vector wrapped in Option. It returns Some(element) if the vector is not empty, None otherwise. This operation has O(1) complexity because it only modifies the length without reallocation. It is the counterpart of push() for LIFO (stack) operations."}},{"@type":"Question","name":"Which method allows concatenating two Strings or adding a &str to a String?","acceptedAnswer":{"@type":"Answer","text":"push_str() adds a &str to the end of an existing String. The + operator can also be used but consumes the left String. format!() allows concatenating without consuming but creates a new String. push_str() is preferable for efficiency as it modifies in place without creating new allocation."}},{"@type":"Question","name":"How to check if a HashSet contains a specific value?","acceptedAnswer":{"@type":"Answer","text":"The contains() method checks if a value exists in the HashSet in O(1) on average. It takes a reference to the searched value and returns a boolean. This operation uses the hash of the value to quickly locate the potential entry then compares with Eq to confirm presence."}},{"@type":"Question","name":"How to transform each element of a vector and collect the results?","acceptedAnswer":{"@type":"Answer","text":"The iter().map(|x| ...).collect() chain transforms each element. iter() creates an iterator over references, map() applies a transformation, and collect() gathers the results. For owned types, into_iter() consumes the vector. This functional approach is idiomatic in Rust."}},{"@type":"Question","name":"What is the difference between iter(), iter_mut() and into_iter()?","acceptedAnswer":{"@type":"Answer","text":"iter() produces immutable references (&T), iter_mut() mutable references (&mut T), and into_iter() consumes the collection and produces owned values (T). The choice depends on the need: read-only, in-place modification, or ownership transfer. into_iter() is called implicitly in for item in collection."}},{"@type":"Question","name":"How to remove a value from a HashMap by its key and retrieve the removed value?","acceptedAnswer":{"@type":"Answer","text":"The remove(&key) method removes the entry associated with the key and returns Option. It returns Some(value) if the key existed, None otherwise. The passed key is a reference, not an owned value. To remove and get the key-value pair, use remove_entry(&key) which returns Option<(K, V)>."}}]}