String Processing, Parsing, And Output Formatting

What's being tested

This tests string parsing, canonicalization, and exact output construction under edge cases, plus efficient lookup-based matching for palindrome pair variants. Interviewers look for clean decomposition into helpers like isPalindrome, splitQuery, formatRow, and for reasoning about correctness, complexity, and malformed inputs.

Patterns & templates

• Palindrome pair lookup — store reversed words in a HashMap; test every split with isPalindrome(prefix/suffix); target O(total_chars * word_len).

• Trie-based palindrome matching — insert reversed words into a trie, carrying palindrome-suffix indices; improves repeated prefix matching but increases implementation risk.

• Delimiter-aware parsing — scan character-by-character instead of blind split('&') when quotes, empty values, or escaped delimiters may appear.

• Type inference parser — normalize values in order: quoted string, boolean flag, integer/float, raw string; document ambiguous cases like 001.

• Duplicate-key accumulation — map key -> value for first occurrence, then promote to key -> list; keep insertion order if output is tested.

• Fixed-width formatting — compute column widths first, then render with ljust/padding; verify borders, trailing spaces, and empty-cell behavior exactly.

• State encoding — for key/path variants, represent visited state as (position, keyMask); BFS gives shortest path in O(V * 2^K + E * 2^K).

Common pitfalls

Pitfall: Treating palindrome pairs as only word + reverse(word) misses split cases like "lls" + "s" and empty-string combinations.

Pitfall: Using naive split('=') or split('&') breaks quoted values, missing values, boolean flags, and duplicate parameters.

Pitfall: Output-formatting problems often fail on whitespace, not logic; compare exact strings and test single row, empty input, and uneven columns.

Practice these

The practice cards below cover the canonical variants — solve all of them and time yourself.