String Patterns

Searching for patterns within strings is a fundamental text processing task. Rust's standard library provides several powerful methods for finding substrings, checking prefixes and suffixes, and locating specific patterns within text.

Pattern Matching Methods

Rust's str type offers these key pattern-matching methods:

  1. .starts_with(pattern) - Check if a string begins with a pattern
  2. .ends_with(pattern) - Check if a string ends with a pattern
  3. .contains(pattern) - Check if a pattern exists anywhere in the string
  4. .find(pattern) - Find the first occurrence, returns Option<usize> (byte index)
  5. .rfind(pattern) - Find the last occurrence, returns Option<usize> (byte index)
  6. .matches(pattern) - Iterate over all matches of a pattern
  7. .match_indices(pattern) - Iterate over matches with their byte positions

These methods accept various pattern types: &str, char, or closures that take a char and return bool.

let text = "hello world, hello universe";
 
// Prefix/suffix checks
assert!(text.starts_with("hello"));
assert!(text.ends_with("universe"));
 
// Finding patterns
assert!(text.contains("world"));
assert_eq!(text.find("hello"), Some(0));
assert_eq!(text.rfind("hello"), Some(13));
 
// Counting matches
assert_eq!(text.matches("hello").count(), 2);

Working with Indices

The .find() and .rfind() methods return byte indices, not character indices. For ASCII strings these are the same, but for Unicode strings you need to be careful:

let text = "café";
// byte index, not char index
assert_eq!(
    text.find('é'),
    Some(3)
);

Your Task

Implement the following functions for string pattern matching:

  1. has_prefix(s: &str, prefix: &str) -> bool - Check if string starts with the given prefix
  2. has_suffix(s: &str, suffix: &str) -> bool - Check if string ends with the given suffix
  3. find_first(s: &str, pattern: &str) -> Option<usize> - Find first occurrence of pattern (byte index)
  4. find_last(s: &str, pattern: &str) -> Option<usize> - Find last occurrence of pattern (byte index)
  5. count_occurrences(s: &str, pattern: &str) -> usize - Count how many times pattern appears
  6. find_all_indices(s: &str, pattern: &str) -> Vec<usize> - Find all byte indices where pattern occurs
  7. extract_between(s: &str, start: &str, end: &str) -> Option<String> - Extract text between first occurrence of start and end markers

Examples

 
// has_prefix
assert!(has_prefix("hello world", "hello"));
assert!(!has_prefix("hello world", "world"));
// empty prefix matches empty string
assert!(has_prefix("", ""));
 
// has_suffix
assert!(has_suffix("hello world", "world"));
assert!(!has_suffix("hello world", "hello"));
assert!(has_suffix("test.rs", ".rs"));
 
// find_first
assert_eq!(find_first("hello hello", "hello"), Some(0));
assert_eq!(find_first("hello world", "xyz"), None);
assert_eq!(find_first("abcabc", "bc"), Some(1));
 
// find_last
assert_eq!(find_last("hello hello", "hello"), Some(6));
assert_eq!(find_last("hello world", "o"), Some(7));
assert_eq!(find_last("test", "xyz"), None);
 
// count_occurrences
assert_eq!(count_occurrences("abababab", "ab"), 4);
assert_eq!(count_occurrences("hello world", "o"), 2);
assert_eq!(count_occurrences("test", "xyz"), 0);
 
// find_all_indices
assert_eq!(
    find_all_indices("abcabc", "abc"),
    vec![0, 3]
);
assert_eq!(
    find_all_indices("hello", "l"),
    vec![2, 3]
);
assert_eq!(
    find_all_indices("test", "xyz"),
    vec![]
);
 
// extract_between
assert_eq!(
    extract_between(
        "<tag>content</tag>",
        "<tag>",
        "</tag>"
    ),
    Some("content".to_string())
);
assert_eq!(
    extract_between("hello [world] test", "[", "]"),
    Some("world".to_string())
);
assert_eq!(
    extract_between("no markers here", "[", "]"),
    None
);

Hints
Click here for hints
  • For has_prefix and has_suffix, use .starts_with() and .ends_with() directly
  • For find_first and find_last, use .find() and .rfind()
  • For count_occurrences, use .matches(pattern).count()
  • For find_all_indices, use .match_indices(pattern) and collect the indices
  • For extract_between:
    1. Use .find() to locate the start marker
    2. Calculate where the content begins (after the start marker)
    3. Use slicing and .find() again to locate the end marker
    4. Extract the substring between them