#1647 - Minimum Deletions to Make Character Frequencies Unique

Medium • View on LeetCode • View on GitHub

Problem Description

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

/**
 * @param {string} s
 * @return {number}
 */
var minDeletions = function(s) {
  const charFrequencies = new Array(26).fill(0);
  for (const char of s) {
    charFrequencies[char.charCodeAt(0) - 97]++;
  }

  charFrequencies.sort((a, b) => b - a);
  let result = 0;
  const usedFrequencies = new Set();

  for (const freq of charFrequencies) {
    if (freq === 0) break;
    let currentFreq = freq;
    while (usedFrequencies.has(currentFreq) && currentFreq > 0) {
      currentFreq--;
      result++;
    }
    usedFrequencies.add(currentFreq);
  }

  return result;
};