String

LeetCode 1016 note: s has at most 1000 characters, so there are few substrings of any fixed length and a large n must be False; checking from n downward fails fast, or extend up to 30 bits from each start to collect every value <= n

LeetCode 3794 note: one line with slicing; a hand-written two-pointer version must convert the string to a list first

LeetCode 1888 note: rotations become length-n windows over s + s; the window’s mismatches against 0101… are diff, and against 1010… they are n - diff

LeetCode 3694 note: the endpoint is the total displacement minus the removed segment’s displacement; a length-k window tracks that segment and each endpoint goes into a set

LeetCode 3750 note: compare the binary string with its reverse bit by bit; the number of mismatches is the answer

LeetCode 3707 note: accumulate the left score while scanning, with the right side as total minus left; scores are alphabet positions 1 to 26, not ord

LeetCode 394 note: on [ push the current string and count, on ] pop and combine; counts can have several digits

LeetCode 3703 note: repeated replace is O(n^2); a stack of (character, run length) removes k ( plus k ) as soon as they line up

LeetCode 2131 note: pair each word with its reverse on both sides; self-palindromes also pair with each other, and only one leftover can sit in the middle

LeetCode 2264 note: there are only ten candidates, “000” to “999”, so check from “999” down whether each appears

Generating all valid parentheses combinations using backtracking approach

Solving the Valid Parentheses problem using stack-based approach