Problem Statement
Character Frequency Sorter
You're developing a text analysis tool that needs to reorganize characters in a string based on how frequently they appear.
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.
Note that uppercase and lowercase letters are considered different characters.
Examples
Example 1:
Input: s = "tree"
Output: "eert"
Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore "eert" is the answer. Note that "eetr" is also a valid answer.
Example 2:
Input: s = "cccaaa"
Output: "cccaaa"
Explanation: Both 'c' and 'a' appear three times, so both "cccaaa" and "aaaccc" are valid answers. Note that "cacaca" is incorrect, as the same characters must be together.
Example 3:
Input: s = "Aabb"
Output: "bbAa"
Explanation: "bbaA" is also a valid answer, but "Aabb" is incorrect. Note that 'A' and 'a' are treated as two different characters.
Constraints
- 1 <= s.length <= 5 * 10^5
- s consists of uppercase and lowercase English letters and digits
Problem Breakdown
To solve this problem, we need to:
- We need to count the frequency of each character in the string
- Characters with higher frequencies should appear before characters with lower frequencies
- Characters with the same frequency can appear in any order
- The same characters must be grouped together in the result
- A hash map or frequency counter is useful for tracking character frequencies
- Sorting characters by their frequencies is the key operation
String Problems
Learning Objective
Apply string manipulation concepts to solve a real-world problem.
Character Frequency Sorter
You're developing a text analysis tool that needs to reorganize characters in a string based on how frequently they appear.
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.
Note that uppercase and lowercase letters are considered different characters.
Examples
Example 1:
'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore "eert" is the answer. Note that "eetr" is also a valid answer.
Example 2:
Both 'c' and 'a' appear three times, so both "cccaaa" and "aaaccc" are valid answers. Note that "cacaca" is incorrect, as the same characters must be together.
Example 3:
"bbaA" is also a valid answer, but "Aabb" is incorrect. Note that 'A' and 'a' are treated as two different characters.
Problem Breakdown
Constraints:
- 1 <= s.length <= 5 * 10^5
- s consists of uppercase and lowercase English letters and digits
Key Insights:
We need to count the frequency of each character in the string
Characters with higher frequencies should appear before characters with lower frequencies
Characters with the same frequency can appear in any order
The same characters must be grouped together in the result
A hash map or frequency counter is useful for tracking character frequencies
Sorting characters by their frequencies is the key operation
Real-World Application
This problem has several practical applications:
Text Analysis
Analyzing character distribution in texts for linguistic research or cryptography.
Data Compression
Frequency-based encoding schemes like Huffman coding use character frequencies for efficient compression.
Natural Language Processing
Preprocessing text data for NLP algorithms by identifying common patterns.
Information Retrieval
Analyzing term frequencies in documents for search engine optimization.