Breadth-First-Search

LeetCode 965 note: every value must equal the root’s; compare values while recursing, not the booleans the recursion returns

LeetCode 783 note: a BST’s in-order is ascending, so the minimum difference is between in-order neighbors; remember the previous value and compare

LeetCode 733 note: DFS or BFS from the start, recoloring 4-directional cells that share the start’s original color; return immediately if the colors are equal

LeetCode 637 note: level-order traversal, dividing each level’s sum by its count

LeetCode 559 note: depth is 1 plus the deepest child, or 1 with no children

LeetCode 530 note: a BST’s in-order is ascending, so the minimum difference is between in-order neighbors; remember the previous value and compare

LeetCode 463 note: each land cell contributes 4 edges, minus 2 for each land neighbor above or to the left

LeetCode 404 note: tell each child during DFS whether it is a left child, adding only left children that are leaves

LeetCode 226 note: swap every node’s children, using a simultaneous assignment so the already-changed side is not reused

LeetCode 112 note: subtract each value from targetSum on the way down; it works if the remainder matches at a leaf

LeetCode 111 note: minimum depth must end at a leaf; with only one child, the empty side (depth 0) cannot count as the minimum

LeetCode 104 note: depth is 1 plus the larger subtree depth, with 0 for an empty tree