Union-Find

Introduction to Union Find

LeetCode 3493 note: convert each row to a set, compare intersection sizes pairwise to add edges, then count components

LeetCode 695 note: DFS each unvisited 1 to measure its island and keep the maximum; cells are the integer 1, not a string

LeetCode 128 note: put everything in a set and count upward only from values whose x - 1 is absent; each value is seen at most twice, O(n)