Binary-Search-Tree

LeetCode 99 note: find the inversions in the in-order sequence: the earlier node of the first inversion and the later node of the last one were swapped

LeetCode 450 note: once the node is found: with zero or one child, splice the child in; with two, copy the right subtree’s minimum and delete that node

LeetCode 449 note: for a BST, pre-order without null markers is enough; deserialize recursively with bounds in O(n)

LeetCode 701 note: walk down the BST to an empty spot and attach the new node; an empty tree must return the new node

LeetCode 173 note: flattening to an array is simple but uses O(n) space; the follow-up keeps the left spine on a stack for amortized O(1) and O(h) space

LeetCode 1373 note: a post-order traversal returns (sum, min, max, is_bst); a node roots a BST when the left max < its value < the right min

LeetCode 109 note: take the middle found with fast and slow pointers as the root and recurse on both halves; the height balances naturally

LeetCode 98 note: every node has a valid range (low, high); going left the upper bound becomes the node and going right the lower bound does; comparing parent and child is not enough

LeetCode 230 note: a BST’s in-order traversal is ascending, so stop an iterative in-order walk at the k-th node

LeetCode 938 note: prune with the BST order, going only right below low and only left above high, adding nodes inside the range

LeetCode 897 note: in-order traversal appending nodes to a right-only chain with left children cleared; keep the dummy separate from the moving tail

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