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Quick Summary

Filter an input character array by excluding characters found in a separate ignore list.
Verify if the remaining sequence reads identically forwards and backwards.
Optimize space usage by avoiding upfront array copying during the filtering process.

What This Tests

Two-pointer technique for symmetric traversal
Efficient membership testing using hash-based lookups
In-place validation logic with minimal auxiliary space
Handling edge cases like completely filtered or single-character results

Common Patterns

Two Pointers

Hashing

Test Cases

Input

Output

Expected