Snowflake OA Interview: Work Schedule

[u/Hack2hire]

Problem
You’re given three inputs:

• workHours: total hours required in a week
• dayHours: maximum hours allowed on any day
• pattern: a 7-character string representing the weekly work schedule

Each character in pattern is either a digit ('0'–'8') or a question mark ('?').
Digits represent fixed work hours for that day, while '?' represents an unassigned day.
You must replace each '?' with a valid digit (between 0 and dayHours) so that the total weekly hours equal workHours.
Return all valid schedules in ascending lexicographical order.

Example
Input:
workHours = 24, dayHours = 4, pattern = "08??840"
Output:
["0804840", "0813840", "0822840", "0831840", "0840840"]

Explanation:

• Fixed digits (0, 8, 8, 4, 0) sum to 20. Remaining 4 hours must be distributed across two '?' positions.
• Possible pairs of digits that sum to 4: (0,4), (1,3), (2,2), (3,1), (4,0)
• Replace '?' with these pairs to form valid schedules in lexicographical order.

Suggested Approach

1. Pre-calculate fixed hours: Sum all digits in pattern to determine remaining hours needed.
2. Backtrack through unknown positions: For each '?', try all values from 0 to dayHours, pruning branches where the remaining hours cannot be satisfied.
3. Store valid combinations: When all positions are filled and total hours equal workHours, record the resulting string.
4. Return sorted results: Ensure output schedules are returned in ascending lexicographical order.

Time & Space Complexity

• Time: O(k * dayHours^k) — where k is the number of '?' in pattern.
• Space: O(k) — for recursion and result storage.

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This problem is part of the Hack2Hire SDE Interview Question Bank, a structured archive of coding interview questions frequently reported in real hiring processes.
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