String

LeetCode 17 note: each level handles one digit and tries its letters; an empty input returns an empty list

LeetCode 1189 note: each letter supports count // needed balloons, with l and o needed twice; take the minimum

LeetCode 1160 note: a word is formable when none of its character counts exceeds chars’; sum the lengths of such words

LeetCode 1108 note: replace every . with [.]

LeetCode 1078 note: split into words and check every three consecutive words, collecting the third when the first two match

LeetCode 1047 note: if the stack top equals the current character both vanish, otherwise push it; after a removal the new top may cancel with the next character

LeetCode 1021 note: track depth instead of a stack; the ‘(’ raising depth from 0 to 1 and the ‘)’ lowering it from 1 to 0 are outermost, everything else stays

LeetCode 1002 note: count each word and intersect all Counters (minimum count per character), then expand

LeetCode 953 note: map letters to their alien index and compare each adjacent pair at the first differing character; with no difference, the shorter must come first

LeetCode 944 note: take each column with zip(*strs) and count the columns that are not non-decreasing

LeetCode 942 note: two pointers hold the smallest and largest unused values; place the smallest on I and the largest on D

LeetCode 929 note: split at @, normalize only the local part (drop everything after +, remove dots), rejoin with the domain and collect in a set