Sort characters by frequency

Hash Table String Sorting Heap (Priority Queue) Bucket Sort Counting

75.1% acceptance

Jan 13, 2026

9174

333

Given a string s, sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers, return any of them.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

use std::collections::HashMap;

impl Solution {
  pub fn frequency_sort(s: String) -> String {
    let mut freq = HashMap::new();
    for c in s.chars() {
      *freq.entry(c).or_insert(0) += 1;
    }
    
    let mut chars: Vec<(char, i32)> = freq.into_iter().collect();
    chars.sort_by(|a, b| b.1.cmp(&a.1));
    
    let mut result = String::new();
    for (c, count) in chars {
      for _ in 0..count {
        result.push(c);
      }
    }
    result
  }
}