Minimum deletions to make character frequencies unique

Hash Table String Greedy Sorting

61.4% acceptance

Feb 25, 2026

5051

A string s is called good if there are no two different characters in s that have the same frequency. Given a string s, return the minimum number of characters you need to delete to make s good. The frequency of a character in a string is the number of times it appears in the string. For example, in the string "aab", the frequency of 'a' is 2, while the frequency of 'b' is 1.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

use std::collections::HashSet;

impl Solution {
  pub fn min_deletions(s: String) -> i32 {
    let mut freq = [0i32; 26];
    for b in s.bytes() {
      freq[(b - b'a') as usize] += 1;
    }
    let mut freq: Vec<i32> = freq.into_iter().filter(|&f| f > 0).collect();
    freq.sort_unstable_by(|a, b| b.cmp(a));
    let mut used: HashSet<i32> = HashSet::new();
    let mut deletions = 0;
    for mut f in freq {
      while f > 0 && used.contains(&f) {
        f -= 1;
        deletions += 1;
      }
      if f > 0 {
        used.insert(f);
      }
    }
    deletions
  }
}