Majority frequency characters

Hash Table String Counting

67.1% acceptance

Feb 25, 2026

You are given a string s consisting of lowercase English letters. The frequency group for a value k is the set of characters that appear exactly k times in s. The majority frequency group is the frequency group that contains the largest number of distinct characters. Return a string containing all characters in the majority frequency group, in any order. If two or more frequency groups tie for that largest size, pick the group whose frequency k is larger.

Solution

Rust

Time O(n log n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn majority_frequency_group(s: String) -> String {
    use std::collections::HashMap;
    let mut freq: HashMap<char, usize> = HashMap::new();
    for c in s.chars() { *freq.entry(c).or_insert(0) += 1; }
    // Group characters by their frequency
    let mut groups: HashMap<usize, Vec<char>> = HashMap::new();
    for (&c, &f) in &freq {
      groups.entry(f).or_default().push(c);
    }
    // Find the group with max size; tiebreak by higher frequency k
    let (_best_k, best_chars) = groups.iter()
      .max_by(|(k1, v1), (k2, v2)| {
        v1.len().cmp(&v2.len()).then(k1.cmp(k2))
      })
      .unwrap();
    let mut result: Vec<char> = best_chars.clone();
    result.sort();
    result.into_iter().collect()
  }
}