The Password Builder

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
Asked in
Rally Health

Problem

Given a positive integer length and a non-empty string pool, return a string of length characters where position i is pool[i % len(pool)].

Random characters, fixed rules.

Example

Input:

length = 8, pool = "abcXYZ"

Output:

"abcXYZab"

Worked solution and explanation

Why this problem exists in real interviews

This tests modular arithmetic for cyclic indexing, a basic but essential skill. It checks whether candidates can cycle through a character pool using the modulo operator without falling back to complex conditional logic.

Break down the requirements

Step 1: Iterate for the requested length

Loop from 0 to length-1, building one character per iteration.

Step 2: Index the pool with modulo

Use pool[i % len(pool)] to wrap around when i exceeds the pool length.

Step 3: Join and return the result

Collect characters in a list and join them into a string.

The solution

Cyclic pool indexing with modulo
def generate_password(length, pool):
    chars = []
    for i in range(length):
        chars.append(pool[i % len(pool)])
    result = ''.join(chars)
    return result

Common follow-up questions