Strings mind map
Character arrays, parsing, and string algorithms.
Core idea: Choose the unit—character, token, or prefix—then treat text as a structured sequence.
Mnemonic: Normalize → bound → parse · Cost: O(n) scan · alphabet state
Normalize: Canonical comparison
Signal: Formatting differs, but identity should not.
Move: Fold case and spacing, or compare a frequency signature instead of raw text.
Examples: Valid Palindrome, Valid Anagram, Group Anagrams
Cover: Character window
Signal: A longest or shortest valid substring must stay contiguous.
Move: Grow counts, then shrink from the left while the constraint still holds.
Examples: Minimum Window Substring, Longest Unique Substring, Find Anagrams
Parse: Stack & state machine
Signal: Nested syntax, operators, escapes, or unfinished frames.
Move: Let each token update explicit state; push context that must resume later.
Examples: Decode String, Basic Calculator, Simplify Path
Segment: Prefix choices
Signal: The string must be split into legal words or palindromes.
Move: Choose a valid prefix, then solve or memoize the remaining suffix.
Examples: Word Break, Palindrome Partitioning, Text Justification