use std::collections::HashSet;
// Finds the last repeated character in a string.
// Scans the string from right to left and returns the first character
// that has already been encountered. Returns None if no character is repeated.
fn find_last_repeated_character(s: &str) -> Option<char> {
// Collect into a Vec<char> to properly handle Unicode scalar values
// and enable reverse iteration.
let chars: Vec<char> = s.chars().collect();
let mut seen = HashSet::new();
// Traverse the characters from right to left
for &c in chars.iter().rev() {
// HashSet::insert returns false if the value was already present in the set
if !seen.insert(c) {
return Some(c);
}
}
None
}
fn main() {
let test_cases = [
"abca",
"abcbd",
"abcde",
"abcdxypcbop",
"abcdxypcbadom",
];
for tc in test_cases {
// Unwrap Option, printing ' ' if no repeated character is found (matching C++ style)
let result = find_last_repeated_character(tc).unwrap_or(' ');
println!("findLastRepeatedCharacter({:?}) -> {}", tc, result);
}
}
/*
run:
findLastRepeatedCharacter("abca") -> a
findLastRepeatedCharacter("abcbd") -> b
findLastRepeatedCharacter("abcde") ->
findLastRepeatedCharacter("abcdxypcbop") -> p
findLastRepeatedCharacter("abcdxypcbadom") -> d
*/
