Hash-Table

LeetCode 997 note: the judge is trusted by the other n - 1 people and trusts nobody, so in-degree minus out-degree equals n - 1

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

LeetCode 961 note: the other n values are distinct, so the first value seen twice is the answer

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

LeetCode 914 note: every card count must be divisible by one X >= 2, i.e. the GCD of all counts is at least 2

LeetCode 888 note: equal sums after swapping x and y means y = x + (sumB - sumA) / 2; put B in a set and check each x from A

LeetCode 884 note: count words across both sentences together; those appearing exactly once are the answer

LeetCode 859 note: lengths must match; identical strings need a repeated character; otherwise exactly two positions differ and cross-match

LeetCode 819 note: replace punctuation with spaces, lowercase, split, count, and pick the most frequent word not banned

LeetCode 804 note: translate each word into a Morse string and count the distinct results with a set

LeetCode 771 note: put jewels in a set and count how many stones are in it