Limit tree height by deleting nodesCodingYou are given a rooted N-ary tree. Every node has a unique integer id. The tree is passed as children: dictint, listint (a node with no entry has no children) together with the…
Last asked Oct 2026
#trees
Merge two config trees with per-node merge rulesCodingTwo configuration files have been parsed from YAML into trees of dicts, lists and plain values: a base and an overlay. Merge the overlay into the base. Each node can carry its own…Last asked Oct 2026
+1Lowest common manager in an org chartCodingA company's reporting structure is a rooted tree. Each person is an Employee with a unique name and a list reports of the people who report to them directly. The root is the CEO…Last asked Oct 2026
Rebuild a task tree from parent-child records and print itCodingYou get a list of task records, each naming a task and its parent. Rebuild the hierarchy of tasks and subtasks and print it as a text tree with connector characters, in the exact…Last asked Sep 2026- Build reporting trees from employee-manager pairsCodingYou get a list of employee, manager pairs, where each person is a positive integer id and the pair means the employee reports directly to that manager. Build the org chart…Last asked Sep 2026
- Binary search tree keys within a rangeCodingGiven a binary search tree (as a level-order list with nulls for missing children) and an inclusive range low, high, return every key in the range in ascending order. Skip the…Last asked Sep 2026
Toy language type inference with generics and tuplesCodingA small typed language has three kinds of type: - Primitives: int, float, char. - Generics: placeholders named T followed by a number (T1, T2, ...). A generic can stand for any…Last asked Sep 2026
+1Customer revenue with referral credit and bottom-k queryCodingBuild an in-memory system that tracks how much revenue each customer brings in, including revenue from the customers they referred. Customers get integer ids starting at 0, in the…Last asked Sep 2026- +1Unix find command with pluggable filtersCodingImplement a small version of the Unix find command over an in-memory file system. The file system holds directories and files. Each file has a name and a size in bytes. Its…Last asked Sep 2026
- Delete leaves with a target value, repeatedlyCodingGiven a binary tree and a target value, delete every leaf that holds the target. If that turns its parent into a leaf holding the target, delete the parent as well, and keep going…Last asked Sep 2026
- Lowest common ancestor in a binary search treeCodingGiven a binary search tree and two distinct keys that are both in it, return their lowest common ancestor: the deepest node whose subtree contains both. A node's subtree includes…Last asked Sep 2026
Binary tree vertical order traversalCodingReturn a binary tree's values column by column, from the leftmost column to the rightmost. The root is in column 0, a left child one column to the left of its parent and a right…Last asked Sep 2026- Range sum of a binary search treeCodingGiven a binary search tree and two bounds low and high, return the sum of the values within the inclusive range, skipping subtrees that cannot contain any. Follow-up: answer many…Last asked Sep 2026
- +1Lowest common ancestor of a binary treeCodingGiven a binary tree (no ordering on the values) and two of its nodes, return their lowest common ancestor: the deepest node that has both in its subtree.Last asked Sep 2026
- Path between two nodes of an implicit Fibonacci treeCodingA Fibonacci tree of order k is a binary tree defined recursively: - Orders 0 and 1 are a single node. - For k = 2, the root's left subtree is a Fibonacci tree of order k - 2 and…Last asked Sep 2026
- Minimum-cost encryption of a directory treeCodingA storage service keeps a filesystem as a tree: Compliance requires every file in the tree to end up encrypted. You can issue two kinds of calls: - encrypt(filepath)Last asked Sep 2026
- Rewrite a SQL query plan treeCodingA query plan is a tree of scan, filter, project and join nodes. Write rewrite rules that make it cheaper, such as moving a filter beneath a join, while the new plan still returns…Last asked Sep 2026
- +1Count and map a cluster tree with message passingCodingA cluster of n machines is wired as a rooted tree (any number of children per node). Each machine knows only three things: its own id (a string such as "4"), its parent's id ("-1"…Last asked Sep 2026
Filter an n-ary tree by substring and render it indentedCodingEach node of an n-ary tree has a string value and a list of children. 1. Given a search string, return the filtered tree: keep every node whose value contains the substring, plus…Last asked Sep 2026- Simplify an arithmetic expression treeCodingYou get the root of an expression tree: every internal node is a binary operator with two children, and every leaf is an integer constant or a variable name. Return a simplified…Last asked Sep 2026
- Throne inheritance without an initial kingCodingModel a royal family's line of succession: people are born to parents, people die, and you return the current order of inheritance (a pre-order walk of the family tree that skips…Last asked Sep 2026
Validate a hierarchy and compute how long a message takes to spreadCodingGiven manager-report relationships, first check that they form a valid hierarchy (one root, no cycles, everyone reachable). Then, if passing a message down each link takes a known…Last asked Sep 2026
Parse HTML into an element tree and query itCodingYou are asked to "write an HTML parser" with no definition of the input, the output or the edge cases. Part of the exercise is pinning that down: ask for examples, then write down…Last asked Aug 2026- Compute entity sizes and validate a hierarchical file systemCodingFiles and folders form a hierarchy. Compute the size of any entity, where a folder's size is the total of everything inside it, and validate the hierarchy: check that it really is…Last asked Aug 2026
- Kth smallest value in a binary search treeCodingReturn the kth smallest value in a binary search tree.Last asked Aug 2026
- Format a forest of nested commentsCodingGiven comments where each one may reply to another, format the whole forest of threads so that every reply appears nested under its parent.Last asked Aug 2026
Print each tree node's level and whether it is balancedCodingGiven a tree, walk it with a depth-first search and report, for every node, its level and whether the subtree under it is balanced (by the definition the interviewer gives, such…Last asked Aug 2026- Sum root-to-leaf numbersCodingEach node of a binary tree holds a digit, so every root-to-leaf path spells a number. Return the sum of all those numbers.Last asked Aug 2026
XOR random number generator to encrypt and decrypt a treeCoding1. Implement a pseudo-random number generator whose state update uses bitwise XOR (shifts and XORs on an integer state), seeded so the same seed always gives the same sequence. 2…Last asked Aug 2026
Serialize and deserialize an N-ary treeCodingDesign a string format for a rooted tree in which each node has any number of children in a fixed order. Implement serialize(root) and deserialize(data) so that decoding gives…Last asked Jul 2026
Inherited permissions across teams, folders and filesCodingDesign a permission system for a workspace organized as a hierarchy of teams, folders, and files. - A team is a root. It can contain folders and files. - A folder sits inside a…Last asked Jul 2026- +2Vertical order traversal of a binary treeCodingGive every node of a binary tree a column (root at 0, left child one less, right child one more) and a row. Return the node values column by column from left to right, top to…Last asked Jun 2026
- Build a quadtreeCodingA quadtree splits a 2D region into four quadrants, recursively: every node is either a leaf or has exactly four children. Build one yourself. One version builds it from a square…Last asked Jun 2026
- Lowest common ancestor in a BST and in a binary treeCodingGiven two nodes, return their lowest common ancestor first in a binary search tree, using the ordering, and then in a plain binary tree where you cannot rely on it. Explain both…Last asked Jun 2026
- Kth largest perfect binary subtreeCodingIn a binary tree, find every subtree that is a perfect binary tree and return the size of the kth largest.Last asked Jun 2026
- Find a pattern across the leaf text of a binary treeCodingEach leaf of a binary tree holds a piece of text. Read from left to right, the leaves spell one long string. Decide whether a given pattern appears in that string, including when…Last asked Jun 2026
- Team with the highest average salary in an org chartCodingGiven an org chart where every employee has a salary, find the manager whose team (the manager and everyone below them) has the highest average salary.Last asked Jun 2026
- Longest path of equal-valued tree nodesCodingGiven a binary tree, return the length of the longest path in which every node has the same value. The path may pass through any node and need not include the root; agree with the…Last asked Jun 2026
- Boolean expression tree with leaf flipsCodingA tree's leaves hold true or false and its inner nodes are boolean operators. Evaluate the tree, then find the fewest leaf flips that make the root come out to a wanted value.Last asked Jun 2026
- +1Convert a BST to a sorted circular doubly linked listCodingRearrange a binary search tree in place into a circular doubly linked list in sorted order, reusing the left and right pointers as previous and next. Do an in-order traversal that…Last asked Jun 2026
- +1All nodes at distance K in a binary treeCodingGiven a binary tree, a target node and k, return every node exactly k edges away from the target. Add parent links (or turn the tree into an undirected graph), then search outward…Last asked Jun 2026
- Build a weighted binary tree from character countsCodingGiven a string s of letters ('A'-'Z', 'a'-'z'; case matters), build a binary tree that summarizes how often each character appears. Each node has three fields: ch, count, and two…Last asked Jun 2026
- Pick the root that needs the fewest edge reversalsCodingYou are given a tree with n nodes labeled 1 to n. Its n - 1 edges are directed: each edge (u, v) points from u to v. Ignoring direction, the edges connect all nodes into a tree…Last asked May 2026
- Validate a parent-child forestCodingGiven a list of parent-child pairs, decide whether they form a valid forest: no node has two parents, there are no cycles, and every tree has one root. Return the reason when it…Last asked May 2026
- Palindromic paths from a node to the rootCodingA storage system keeps its directories in a tree. Each directory holds one lowercase letter as a label. You are given: - arr: a list of n lowercase letters; arri is the label of…Last asked May 2026
- +1Diameter of a binary treeCodingReturn the number of edges on the longest path between any two nodes of a binary tree. The path need not pass through the root. Solve it in one pass.Last asked May 2026
- Merge two named treesCodingEach tree node is a dictionary with a name, an integer value and an ordered list of children. Given two such trees t1 and t2, build a new merged tree that follows t1's nodes and…Last asked May 2026
- Flower placement and directory deletionCodingTwo problems in one round: 1. A row of plots has some flowers planted already, and no two flowers may be next to each other. Decide whether n more flowers can be planted. 2. Given…Last asked May 2026
- Longest consecutive sequence path in a binary treeCodingReturn the length of the longest parent-to-child path in a binary tree in which each value is exactly one more than the value before it. Follow-up: the path may go in any…Last asked Apr 2026
- Quickselect, distance between tree nodes, and substrings with a prefixCodingThree problems from one loop: 1. Find the k-th largest element with quickselect. Compare the approaches and how to choose the pivot, then implement one. 2. Given the edges of a…Last asked Apr 2026
- +1Binary tree right side viewCodingReturn the values visible when you look at a binary tree from the right: the last node of each level, top to bottom. Follow-ups: the left side view, and both views in a single…Last asked Apr 2026
- Validate a binary search treeCodingDecide whether a binary tree is a valid binary search tree.Last asked Apr 2026
- +1Binary tree zigzag level-order traversalCodingReturn a binary tree's values level by level, alternating direction: left to right on the first level, right to left on the next, and so on. Use a BFS by levels and reverse (or…Last asked Apr 2026
- Siblings, cousins or neither: two nodes in a treeCodingGiven a tree and two of its nodes, say whether they are siblings (same parent), cousins (same depth, different parents) or neither.Last asked Apr 2026
- +1Serialize and deserialize a binary treeCodingTurn a binary tree into a string and rebuild the identical tree from that string. Choose a format (pre-order with null markers, or level order), handle empty trees and negative…Last asked Apr 2026
- Build a binary tree from parent-child descriptionsCodingEach description gives a parent value, a child value, and whether the child is the left or right child. Build the binary tree and return its root.Last asked Mar 2026
List every file path in a directory treeCodingGiven a directory tree (folders containing files and other folders), return the full path of every file. Write it with a depth-first search, then discuss an iterative version and…Last asked Mar 2026- Construct a BST from its preorder traversalCodingGiven the preorder traversal of a binary search tree with distinct values, rebuild the tree and return its root. Aim for linear time.Last asked Mar 2026
- Serialize an expression tree with the fewest parenthesesCodingGiven a binary expression tree of numbers and operators, print it as an infix expression using only the parentheses that precedence and associativity require (for example, keep…Last asked Feb 2026
- Kth smallest element in a BSTCodingGiven the root of a binary search tree and an integer k, return the k-th smallest value in it, ideally stopping the in-order walk as soon as you reach it.Last asked Feb 2026
- Manager and peer relationships with is_manager queriesCodingImplement three functions: - manager(a, b): a is the manager of b. - peer(a, b): a and b have the same manager. - ismanager(a, b): return whether a is a manager of b. Decide how…Last asked Feb 2026
- Populate next right pointers in each nodeCodingEach node of a binary tree (not necessarily perfect) has a next pointer. Set every node's next to the node to its right on the same level, or null at the end of a level…Last asked Feb 2026
- Python fundamentals: a Fibonacci generator, a balanced BST and frozensetCodingA set of short Python tasks: write a generator that yields the Fibonacci sequence, build a balanced binary search tree (for example from a sorted list), and explain frozenset, how…Last asked Feb 2026
- Check whether a binary tree is completeCodingReturn whether a binary tree is complete: every level is full except possibly the last, and the last level's nodes are as far left as possible.Last asked Feb 2026
- Cheapest common ancestor in a treeCodingNodes of a tree carry costs. Given a set of nodes, find the common ancestor of all of them that has the lowest cost.Last asked Feb 2026
- Lowest common ancestor with parent pointersCodingEach tree node has a pointer to its parent, and you are given only the two nodes, not the root. Return their lowest common ancestor using O(1) extra space.Last asked Feb 2026
- Lazy in-order BST iteratorCodingWrite an iterator over a binary search tree that returns values in sorted order one at a time, with next() and hasnext(). Do it lazily with a stack, so memory is proportional to…Last asked Feb 2026
+2Minimum distance between two nodes in an N-ary treeCodingYou are given the root of an N-ary tree. Every node has an integer val, unique within the tree, and a list children of its direct children. There are no parent pointers…Last asked Feb 2026- Check that a parent array forms a valid treeCodingYou get an array where parenti is the parent of node i (the root has no parent, for example -1). Return whether the array describes one valid tree: exactly one root, no cycles…Last asked Feb 2026
- Populate next pointers in a perfect binary treeCodingIn a perfect binary tree, set each node's next pointer to the node to its right on the same level, or null at the end of a level. Do it with O(1) extra space by walking each level…Last asked Feb 2026
Maximum path sum in an N-ary treeCodingEach node of an N-ary tree holds an integer. A path joins any two nodes through parent and child links and visits each node at most once. Return the largest path sum. Unlike the…Last asked Jan 2026
Time for an infection to spread through a binary treeCodingA binary tree catches fire (or an infection) at one given node. Every minute it spreads to the neighbours of each burning node: its children and its parent. Return how many…Last asked Jan 2026- Binary search tree iteratorCodingImplement an iterator over a binary search tree that returns the values in ascending order with next() and hasnext(). Each call should take amortised O(1) time, and memory should…Last asked Jan 2026
- Sum of distances from every node in a treeCodingGiven an undirected tree with n nodes, return for every node the sum of its distances to all other nodes. A BFS from every node is too slow; compute it in linear time with two…Last asked Jan 2026
- Decide whether two people in a family tree are relatedCodingYou get a family tree as parent and child links. Given two people in it, decide whether they are related through the tree. Agree on what "related" means with the interviewer (for…Last asked Jan 2026
- +3Maximum sum of non-adjacent houses, on a line, a circle and a treeCodingEach house holds some value and you cannot take two neighbours. Find the best total for houses in a row, then for houses arranged in a circle, then for houses arranged as a binary…Last asked Jan 2026
- Resolve user roles across an account hierarchyCodingAccounts form a hierarchy, and users are given roles on accounts. Given the hierarchy and the role assignments, work out the roles a user has on a given account, including roles…Last asked Jan 2026
- Build a binary tree from a parenthesized stringCodingA string encodes a binary tree as an integer followed by zero, one or two parenthesized subtrees, the left one first, for example 4(2(3)(1))(6(5)). Parse it into a tree and return…Last asked Jan 2026
- All root-to-leaf path sumsCodingReturn a list with the sum of the values along every root-to-leaf path of a binary tree, one entry per leaf, in left-to-right order.Last asked Dec 2025
- Lowest common ancestor in an N-ary treeCodingGiven the root of an N-ary tree and two of its nodes, return their lowest common ancestor. Use one depth-first pass in which each subtree reports whether it contains each of the…Last asked Dec 2025
- Mode of a ternary search treeCodingIn this tree each node has up to three children: the left subtree holds smaller values, the middle child equals the node's value, and the right subtree holds larger values. Return…Last asked Nov 2025
- Outer boundary of an N-ary treeCodingPicture walking around an N-ary tree: from the bottom-left up the left side to the root, then down the right side to the bottom-right. Return the nodes seen on that walk, in…Last asked Oct 2025
- Print a directory tree with indentationCodingGiven a root directory, print it and everything under it, one entry per line, with each entry indented one step more than its parent directory.Last asked Oct 2025
- Store words for lexicographic range queriesSystem designDesign storage for a set of words that returns every word in a lexicographic range low, high. For the words aa, aaa, ac, f, z, the range a, b gives aa, aaa, ac and ab, b gives ac…Last asked Oct 2025
Is a sequence a subsequence of a tree's in-order traversal?CodingGiven a binary tree and a sequence of numbers, decide whether the sequence appears, in order, within the tree's in-order traversal (not necessarily next to each other). Walk the…Last asked Sep 2025- +1Left and right views of a binary treeCodingReturn the left view of a binary tree (the first node seen at each level from the left) and the right view (the last node at each level). Write it with breadth-first search, then…Last asked Sep 2025
- Unique visitors per department from click logsCodingEach product has an id, a department, a category and a subcategory; the last three form a parent-child hierarchy. A click log records (customerid, productid). For any department…Last asked Sep 2025
- Root-started value path in an N-ary treeCodingYou are given the root of an N-ary tree (each node has an integer val and a list of children) and a list of integers path. Return true if there is a downward path that starts at…Last asked Sep 2025
- Remove deleted folders and their descendants from a path listCodingYou get a list of hierarchical paths such as California, California/San Francisco and California/San Francisco/7th Street, and a list of paths to delete. Deleting a path removes…Last asked Sep 2025
- Subsets, with and without backtrackingCodingReturn every subset of a set of distinct numbers using backtracking, then write it again iteratively, without backtracking, by building subsets up or using bit masks. Reported in…Last asked Sep 2025
- Sum tree with node values computed from childrenCodingA tree's leaves hold numbers, and every other node's value is the sum of its children. Return the value of any node. Then support changes: turn a node into a leaf with a value, or…Last asked Sep 2025
Implement a trie (prefix tree)CodingImplement a prefix tree over strings: insert a word, check whether a whole word is present, and check whether any stored word starts with a given prefix. Design the classes so…Last asked Aug 2025- Lock, unlock and upgrade nodes in a treeCodingA tree is given by a parent array. Implement lock(node, user), unlock(node, user) and upgrade(node, user): a node can be locked by a user if it is unlocked; unlocked only by the…Last asked Aug 2025
- Delete a node from a binary search treeCodingGiven the root of a binary search tree and a key, delete the node with that key and return the root, keeping it a valid BST. Handle the cases of a leaf, a node with one child, and…Last asked Apr 2025
Block type with the most childrenCodingOver a tree of typed document blocks, find which block type has the most children in total. Reported on 1point3acres' Notion bank; reconstructed in our own words.- Nested todo list with subtasksCodingModel a todo list whose items can nest subtasks to any depth: add, complete and list tasks while keeping the hierarchy. Reported on 1point3acres' Notion bank; reconstructed in our…
- Folder path from a node idCodingA file browser stores its folder hierarchy as three parallel arrays: - idListi is a unique folder id. - childreni lists the ids of the folders directly inside folder idListi. -…
- Peel an N-ary tree one leaf layer per dayCodingEvery day, all leaves of an N-ary tree fall off at the same time. A leaf is a node with no children left. When a node loses its last child, it becomes a leaf and falls on the next…
- Merge two n-ary trees by child positionCodingImplement mergetrees(root1, root2). It takes the roots of two n-ary trees and returns the root of a new tree that merges them. Each node has an integer val and an ordered list…
- +1Root of the largest tree in a forestCodingYou are given a list relations. Each entry child, parent says that parent is the direct parent of child. Together the relations form a forest: there are no cycles, and every node…
- +2Compress an n-ary tree by promoting childrenCodingEach node of an n-ary tree holds a unique integer value and an ordered list of children. You are given the root and a list compressednodes of values. Implement compress(root…