Sort Characters By Frequency
To solve the problem of sorting the characters in the given string s
based on their frequency, we can follow these steps:
 Count Frequencies: Use a dictionary to count the frequency of each character in the string.
 Sort Characters by Frequency: Sort the characters based on their frequency in descending order.
 Build Result: Iterate through the sorted characters and build the result string by repeating each character according to its frequency.
Here’s the code that puts all the steps together:


Example Explanation:
 For
s = "tree"
, the output can be"eert"
as ’e’ appears twice, and ‘r’ and ’t’ both appear once.  For
s = "cccaaa"
, the output can be"aaaccc"
as both ‘c’ and ‘a’ appear three times.
The time complexity of this solution is (O(n \log n)), where (n) is the length of the string, since we are sorting the characters based on their frequency. The space complexity is (O(n)) as we are using additional data structures to store the frequency counts.
Define the Terms
Define the Interface
Analyze the Input and Output
Identify the Invariants
Identify the constraints
Search the Problem Space
Classify the Problem
Analyze the Examples
Solve the Problem by Hand
Describe the Pattern
Distill the Observations to Create Insights
Brute Force Approach
[2, 0, 4, 1] 0, 1. 2. 3
Analyze Time and Space Complexity
Outline the Solution
 Frequency array to keep track of the frequency of letter
in the given input, keep track of the most frequent
character location
 Size must be 58 (capital letters are allowed)
 output as array
 Get the highest frequency value, convert the index value to character
 Append to the output
 Decrement the counter
 Repeat until we reach 0
 We can construct the string sequentially
 Return the output array converted to a string
Key Takeaways
 Blindly memorizing coding patterns
 You try to force yourself coding pattern that is not making the code concise.
t => 1 r => 1 e => 2

