Bfs

DFS return values, BFS level order, BST bounds, climbing to the LCA, tree diameter, and leaf trimming

Connected components, grid flood fill, multi-source BFS, state-space BFS, shortest cycles, and recursion depth in DFS

LeetCode 827 note: label every island and record its size, then for each 0 add the sizes of the distinct neighboring islands plus 1

LeetCode 3203 note: connect the two centers; the answer is max(d1, d2, ceil(d1/2) + ceil(d2/2) + 1)

LeetCode 3313 note: the last marked node is the farthest one, and a farthest node can always be a diameter endpoint

LeetCode 2608 note: BFS from every node; a visited neighbor that is not the parent closes a cycle of length dist[u] + dist[v] + 1

LeetCode 987 note: collect (col, row, val) triples, sort them, and group by column

LeetCode 1210 note: the BFS state is (tail position, orientation), each move checks its own empty cells, and equal step costs need no heap

LeetCode 301 note: compute the minimum left and right deletions before backtracking, or BFS one deletion per level and stop at the first valid level

LeetCode 864 note: the BFS state is (position, bitmask of keys), so the same cell with different keys is a different node

LeetCode 323 note: count components with DFS or Union-Find; Union-Find without path compression is much slower

LeetCode 1377 note: undirected edges, seen must hold nodes, and an early arrival depends on whether the frog can still move