The Alphabet Sorter

An easy Python interview practice problem on DataDriven. Write the Python and run it against test cases, with instant feedback.

Domain
Python
Difficulty
easy
Seniority
L3

Problem

Given a list of strings, return a dict whose keys are lowercase first characters and values are lists of strings starting with that character, preserving input order within each group.

Filing cabinet logic: everything goes in its proper drawer.

Example 1

Input:

strings = ["apple","ant","banana","avocado"]

Output:

{"a":["apple","ant","avocado"],"b":["banana"]}

Example 2

Input:

strings = ["cat","cow","dog"]

Output:

{"c":["cat","cow"],"d":["dog"]}

Worked solution and explanation

Why this problem exists in real interviews

Grouping strings by their initial character tests dictionary accumulation with key derivation. It is the same grouping pattern as GROUP BY in SQL, applied to the first character.

Break down the requirements

Step 1: Extract the first character, lowercased

Use word[0].lower() as the grouping key.

Step 2: Accumulate strings per group

Append each string to the list for its initial character, preserving input order.

The solution

Dict accumulation grouped by lowercased initial character
def group_by_initial(strings):
    groups = {}
    for s in strings:
        key = s[0].lower()
        if key not in groups:
            groups[key] = []
        groups[key].append(s)
    return groups

Common follow-up questions