Detect whether an (extended) ASCII string is a palindrome anagram using Rust

lib.rs

// Given a string, how do you determine whether it's an anagram of a palindrome?
// Solution: Given the unique set of chars, at most 1 should appear in the string
// an odd number of times.
// chars() returns Unicode Scalar Values, and these might not match up
// with grapheme clusters, so this can't be assumed to work correctly
// for anything other than (extended) ASCII

fn unique_chars(s: &str) -> String {
    let mut v: Vec<char> = s.chars().collect();
    // dedup removes consecutive identical elements, so we need a sort first
    v.sort_unstable();
    v.dedup();
    v.into_iter().collect()
}

/// Count the number of odd occurrences of each unique char in the string
/// If the sum is greater than 1, no palindrome is possible
fn possible_palindrome(letters: &str) -> bool {
    let uniq = unique_chars(letters);
    uniq.chars()
        .map(|char| letters.matches(char).count() % 2)
        .sum::<usize>()
        <= 1
}

fn main() {
    let pal = "ABBBBAF";
    let npal = "DABBAF";
    assert_eq!(possible_palindrome(pal), true);
    assert_eq!(possible_palindrome(npal), false);
}