Array

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 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 941 note: climb from the left to the peak, then descend; you must reach the end exactly, with the peak not at either end

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 922 note: pointers i over even slots and j over odd slots, each stepping by two; when slot i holds an odd number, move j to a misplaced even and swap

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 908 note: lower the maximum by k and raise the minimum by k; the answer is max(0, max - min - 2k)

LeetCode 905 note: a write pointer swaps even numbers to the front, just like move zeroes

LeetCode 896 note: monotonic means non-increasing or non-decreasing; check both directions, allowing equal neighbors

LeetCode 892 note: a stack of v cubes has 4v + 2 faces; subtract 2 × min for each overlap with the stacks above and to the left