What is the strategy to generate all binary strings from a pattern?
Given a pattern containing wildcards, you must generate every possible binary string that matches it. This evaluates your grasp of recursion and backtracking mechanisms.
Why Interviewers Ask This
This question probes your ability to implement recursive solutions and manage state during exploration of a solution space. Google values candidates who can systematically explore possibilities without missing cases or creating infinite loops. It also tests your understanding of backtracking, a critical skill for combinatorial problems often found in real-world applications like parsing or constraint satisfaction.
How to Answer This Question
Explain the recursive function where you process the pattern character by character. If the character is a wildcard, branch into two calls: one assuming '0' and another assuming '1'. If it's a fixed bit, proceed with that specific value. Base case occurs when the pattern is fully processed. Emphasize how backtracking allows you to revert changes and try alternative paths efficiently.
Key Points to Cover
- Use recursion to explore branching possibilities
- Handle wildcards by creating separate branches
- Implement base case when pattern is exhausted
- Ensure no duplicate strings are generated
Sample Answer
I would define a recursive function that takes the current index and the current string built so far. At each step, if the pattern has a '0' or '1', I append it and recurse. If it's a '?', I make two recursive calls: one…
Common Mistakes to Avoid
- Forgetting to handle the base case properly
- Modifying the same string object across recursive calls without copying
- Missing edge cases where the pattern is empty
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