This approach involves using a hash map to count the frequency of each character, followed by sorting the characters by frequency in descending order. Here's how the approach works step-by-step:

1. Use a hash map (or a dictionary) to store the frequency of each character in the string.
2. Convert the hash map to a list of tuples (or a priority queue), where each tuple contains a character and its frequency.
3. Sort this list of tuples primarily by frequency in descending order. If two characters have the same frequency, the order can be arbitrary since any valid ordering is acceptable.
4. Construct the result string by repeating each character in the sorted list according to its frequency.

This approach leverages the Bucket Sort technique where we'll map frequencies to characters directly. This is especially efficient when the range of possible frequencies is low compared to the number of characters.

1. Count the frequency of each character using a fixed-size array (as we are dealing with ASCII).
2. Create an array of buckets, where each bucket at index i stores characters appearing i times.
3. Build the output from the highest frequency bucket to the lowest.