Lowercase characters
Input
merge_sort_string('dbca')
Output
abcd
Characters of the string are sorted using merge sort to produce 'abcd'.
Full lesson preview
Sort characters in a string using merge sort
Implement merge sort to sort the characters of a string and return the sorted string.
Python practice14 minSearching & SortingIntermediateLast updated March 25, 2026
Problem statement
Given a string, sort its characters using the merge sort algorithm and return a new string with characters in non-decreasing order. Treat characters according to their natural Python ordering (i.e., uppercase letters come before lowercase letters by ASCII). Do not use built-in sorted().
Task
Use merge sort to sort the characters of a string and return the resulting string in non-decreasing character order.
Examples
Input format
A single string s.
Output format
A string containing the characters of s sorted in non-decreasing order.
Constraints
- Do not use sorted() or str.sort().
- Use merge sort to achieve O(n log n) time complexity.
- Preserve characters; only their order changes.
Samples
Sample 1
Input
'bbaac'
Output
aabbc
Duplicates are preserved and placed in sorted order.