LeetCode/rs/2024-02-07-sort-characters-by-frequency.rs

use std::cmp;
use std::collections::HashMap;

impl Solution {
    fn get_freqs(s: &str) -> HashMap<char, usize> {
        let mut freqs = HashMap::new();

        for c in s.chars() {
            *freqs.entry(c).or_insert(0) += 1;
        }

        freqs
    }

    pub fn frequency_sort(mut s: String) -> String {
        let mut freqs: Vec<(char, usize)> = Solution::get_freqs(&s).into_iter().collect();
        freqs.sort_by_key(|(_, count)| cmp::Reverse(*count));

        freqs.into_iter().fold(String::new(), |mut s, (c, n)| {
            for _ in 0..n {
                s.push(c);
            }

            s
        })
    }
}