pub fn is_anagram(s: &str, t: &str) -> bool {
let mut freq_s: std::collections::HashMap<char, i32> = std::collections::HashMap::new();
let mut freq_t: std::collections::HashMap<char, i32> = std::collections::HashMap::new();
for c in s.chars() {
*freq_s.entry(c).or_insert(0) += 1;
}
for c in t.chars() {
*freq_t.entry(c).or_insert(0) += 1;
}
freq_s == freq_t
}