Grokking the Coding Interview: Patterns for Coding Questions
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Frequency Sort (medium)

Problem Statement

Given a string, sort it based on the decreasing frequency of its characters.

Example 1:

Input: "Programming"
Output: "rrggmmPiano"
Explanation: 'r', 'g', and 'm' appeared twice, so they need to appear before any other character.

Example 2:

Input: "abcbab"
Output: "bbbaac"
Explanation: 'b' appeared three times, 'a' appeared twice, and 'c' appeared only once.


  • 1 <= str.length <= 5 * 105
  • str consists of uppercase and lowercase English letters and digits.

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