Day 13: Strings

Rust has two main string types, and understanding them is crucial!

String vs &str

Type	Ownership	Mutability	Location
`String`	Owned	Can be mutable	Heap
`&str`	Borrowed	Immutable	Anywhere

let s1: &str = "hello";           // String literal (in binary)
let s2: String = String::from("hello");  // Owned, heap-allocated
let s3: &str = &s2;               // Borrow String as &str

String Operations

let mut s = String::from("hello");

s.push(' ');              // Append char
s.push_str("world");      // Append &str
s += "!";                 // Concat with +=

let combined = format!("{} {}", "hello", "world");

Converting Between Types

// &str → String
let owned = "hello".to_string();
let owned = String::from("hello");

// String → &str
let borrowed: &str = &owned;

Strings in Rust are UTF-8 encoded. Indexing by byte position can be dangerous!

String Methods

let s = "hello world";
s.len()                  // Byte length
s.is_empty()             // Check if empty
s.contains("world")      // Substring check
s.split_whitespace()     // Iterator over words
s.chars()                // Iterator over chars

The Task

Implement reverse_words(s) that reverses the order of words.

Input: "rust is awesome"
Output: "awesome is rust"

Requirements

Split by whitespace
Reverse the order
Join back with spaces

Hints

fn reverse_words(s: &str) -> String {
    s.split_whitespace()
        .rev()
        .collect::<Vec<_>>()
        .join(" ")
}

Or:

let words: Vec<&str> = s.split(' ').collect();
words.into_iter().rev().collect::<Vec<_>>().join(" ")