+1Reachability in a time-indexed train scheduleCodingGiven train departures and arrivals with timestamps, decide whether a destination is reachable from a start station without time travel. Reported on 1point3acres' Glean bank;…
Last asked Oct 2026
#bfs
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+2Concurrent same-host web crawlerCodingImplement a web crawler that finds every page reachable from a start URL on the same host, and fetches pages concurrently. You are given a blocking helper: Write: python def…Last asked Oct 2026
Assign robots to their nearest pickup items on a grid with obstaclesCodingOn an m x n grid with obstacles there are k robots and k items. Send each robot to one item, preferring the item nearest to it by walking distance. Several robots can share the…Last asked Oct 2026
Fewest moves for a chess piece to capture the kingCodingA rectangular board has blocked squares, your piece and the opposing king. Your piece's type decides the directions it may step in, and it can never move onto a blocked square…Last asked Oct 2026
Shortest path through a digit grid with diagonal movesCodingYou are given an m x n grid of digits. A cell holding 0 is a wall; a cell holding 1 through 9 is open. Starting at the top-left cell (0, 0), find a shortest route to the…Last asked Sep 2026- Cell with the least total walking distance to all targets around wallsCodingA grid has targets, empty cells and walls. Walking moves up, down, left or right and cannot cross walls. Find a non-wall cell whose summed walking distance to every target is as…Last asked Sep 2026
Sizes of connected regions in a binary image, in scan orderCodingA binary image is an m x n grid of 0s and 1s. Foreground pixels (1s) that touch up, down, left or right belong to the same region; diagonal neighbours do not. Return the size of…Last asked Sep 2026- Evaluate divisionCodingYou get equations a / b = value between string variables, each standing for a positive real number, and a large batch of queries c / d. Answer every query from the equations, or…Last asked Sep 2026
- Minimum Manhattan distance between X and Y in a matrixCodingFind the smallest Manhattan distance between any X cell and any Y cell in a matrix. Reported on 1point3acres' Glean bank; reconstructed in our own words.Last asked Sep 2026
+3Threshold infection spread on a gridCodingA lab tracks a disease across a rectangular field of cells. You are given an m x n grid where 0 is a healthy cell and 1 is an infected cell, and an integer threshold. Each day…Last asked Sep 2026
+4Group dependent tasks into parallel levelsCodingYou run a build system. Each task has a unique, non-empty lowercase name. Some tasks depend on others: a dependency before, after means before must finish before after can start…Last asked Sep 2026
Explore a friend graph through a remote API with few callsCodingYou cannot read a social graph directly; the only access is getfriends(userid), a remote call that returns a user's friends and costs a network round trip. Write code that…Last asked Sep 2026- Grid reachability for a robot that cannot reverseCodingA robot moves on a grid of open cells, blocked cells, a start S and a destination D. It always faces one of four directions, can never turn around, and may only turn in the ways…Last asked Sep 2026
Grid path from start to target, then the path farthest from a catCodingAn N x N grid has a start cell S, a target cell T, water cells and land cells. You move one step up, down, left or right and can never enter water. 1. Decide whether you can get…Last asked Sep 2026- Shortest path, nodes on any shortest path, and can Alice evade BobCodingYou get an undirected, unweighted graph with n nodes. Alice starts at node a and wants to reach node t. 1. Return the length of the shortest path from a to t. 2. Return every node…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
- Exchange rate between two currencies through chained conversionsCodingYou get a list of rates from, to, rate, each meaning one unit of from is worth rate units of to. Given a source and a target currency, return the rate between them by chaining…Last asked Sep 2026
Fastest single-mode commute on a city gridCodingYou are planning a commute across a city drawn as a 2D grid of characters: - 'S': your starting point (exactly one). - 'D': your destination (exactly one). - '1' to 'k': a block…Last asked Sep 2026
Shortest increasing path to a target value in a gridCodingGiven an integer grid, answer repeated queries. Each query names a target value; return the values along a shortest path from the top-left cell to a cell holding that value, where…Last asked Sep 2026- Grid maze solver with keys, doors and bombs, AI-assistedCodingYou get a small existing codebase that models a grid maze and an AI assistant you may use. Fix a bug in the provided code, then find the shortest path from start to exit, then add…Last asked Sep 2026
- Add one delivery center to minimize the worst distanceCodingA grid marks delivery centers with 1 and every other cell with 0. The distance between two cells is max(x1 - x2, y1 - y2) (moving in all eight directions). The grid's…Last asked Sep 2026
Fewest clicks between two wiki pagesCodingWiki pages link to other pages. Given a start page and a target page, return the fewest clicks needed to get from one to the other, or report that the target can't be reached. You…Last asked Sep 2026- Fewest nodes on a path when one vertex may be brokenCodingFind the path between two nodes of a graph that passes through the fewest nodes, and return that count. One vertex may be broken and unusable: handle both the case where it…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
- Shortest path in a grid with obstacle eliminationCodingA grid has empty cells and obstacles. Find the fewest steps from the top-left to the bottom-right cell moving up, down, left or right, when you may remove up to k obstacles along…Last asked Aug 2026
- Time for grid signals to reach every target, then remove one blockerCodingA grid holds signal sources, targets and blockers. Signals spread from cell to neighboring cell, one step per unit of time, and cannot pass through blockers. 1. Return how long it…Last asked Aug 2026
- +1Shortest distance from all buildingsCodingA grid has empty land, buildings and obstacles. Find the empty cell whose total walking distance to every building is smallest (moving up, down, left or right), or return -1 if no…Last asked Aug 2026
- Services that go down when their dependencies shut downCodingYou get a map of which services depend on which, and a list of services being shut down. A service is unavailable if it is shut down itself or depends, directly or through other…Last asked Aug 2026
- Minesweeper: reveal a regionCodingImplement a click on a Minesweeper board. Clicking a mine ends the game. Clicking a cell with mines around it shows the count. Clicking a cell with none reveals it and spreads to…Last asked Aug 2026
- +1Distance from every desk to its nearest bathroomCodingAn office floor plan is a grid of bathrooms, desks and open floor. For every desk, return how many steps (up, down, left, right) it takes to reach the closest bathroom. Expect…Last asked Jul 2026
Is a graph bipartite?CodingGiven an undirected graph, decide whether its nodes can be colored with two colors so that no edge joins two nodes of the same color. Color with BFS or DFS and look for a…Last asked Jul 2026- Reach a target when you can only step between nearby pointsCodingYou get a set of unordered points, a start point, an end point, and a function getDistance(x, y). You can step from one point to another only when their distance is within 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
- Shortest grid path with one cell conversionCodingFind the length of the shortest path across a grid when you are allowed to convert one blocked cell into an open one along the way.Last asked Jun 2026
Shortest bridge between two islandsCodingA binary grid contains exactly two islands of 1s (4-directionally connected). Return the fewest 0 cells you must flip to 1 to connect them. Find one island with DFS, then expand…Last asked Jun 2026
Fill a layover with the fewest bookingsCodingYou land with a long layover and want to spend all of it on bookable local experiences. Each experience has a fixed whole-number duration in hours, and you may book the same…Last asked Jun 2026- Shortest path in a grid with blocked cellsCodingGiven a grid in which some cells are blocked, return the length of the shortest path from a start cell to a target cell, moving up, down, left or right, or report that no path…Last asked Jun 2026
- Fewest moves across a grid when each move can jump up to k cellsCodingOn a grid with blocked cells, each move goes up, down, left or right by one to k cells, without passing through a blocked cell. Return the fewest moves from the start to the…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
- 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
- Maximum candies from boxes with keysCodingSome boxes are open and some are locked. Each box holds candies, keys to other boxes, and more boxes. You start with a few boxes. You may open a box once you have it and it is…Last asked May 2026
- Sort an array with rotate and flip operationsCodingYou are given an array arr of n distinct integers. You may apply two operations, and each one counts as one step: - Rotate: remove the first element and append it to the end. p…Last asked May 2026
+1Best meeting point on a gridCodingA grid marks several people's (or points') positions. Find the cell that minimizes the total distance to all of them. Start with a brute force (for example a BFS from each point)…Last asked May 2026- Remove invalid parentheses: every minimal resultCodingRemove the minimum number of parentheses from a string so it becomes valid, and return every distinct valid string you can get that way.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
- Blind maze escape: one command sequence for every startCodingA robot is somewhere in a grid maze of walls (), open cells (.) and an exit (E), but you do not know which open cell it starts on. It obeys the commands U, D, L and R, each moving…Last asked Apr 2026
- Sliding puzzle on a 2 by 3 boardCodingA 2 by 3 board holds tiles 1 to 5 and one empty cell. A move slides a tile next to the empty cell into it. Return the fewest moves to reach the solved board, or -1 if it cannot be…Last asked Apr 2026
- +1Island areas and water boundariesCodingYou are given an m x n grid of characters. Each cell is '1' (land) or '0' (water). Land cells that share a side (up, down, left or right) belong to the same island. Diagonal cells…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
- Detonate the most bombs in a chain reactionCodingEach bomb has a position and a blast radius. Setting one off detonates every bomb within its radius, and those set off others in turn. Return the largest number of bombs that can…Last asked Apr 2026
- +1Minimum knight movesCodingOn a chess board (possibly infinite), return the fewest moves a knight needs to get from one square to another. Use BFS, and consider symmetry or bidirectional BFS to make it…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
- +1Score a tile board by connected terrain regionsCodingA tile-laying board game ends when every player has filled a rectangular board. You must compute a player's final score. You are given board, a 2D list of strings with R rows and…Last asked Mar 2026
- +1Max area of islandCodingGiven a binary matrix, return the area of the largest island: a group of 1 cells connected up, down, left or right (diagonals don't connect).Last asked Mar 2026
- Breadth-first web crawler with retriesCodingIn your own IDE, write a crawler that walks a given website breadth-first from a start URL, normalizing URLs and retrying requests that fail. API docs are allowed; AI tools are…Last asked Mar 2026
- Rotting oranges: time for an infection to cover a gridCodingA grid has empty cells, healthy cells and infected cells. Every minute each infected cell infects its healthy neighbors up, down, left and right. Return the minutes until no…Last asked Mar 2026
- Nearest exit from a mazeCodingGiven a grid maze of walls and open cells and your starting cell, return the fewest steps to the nearest exit, an open cell on the border other than the start, or -1 if there is…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
- Time for a virus to infect the whole gridCodingA grid has infected, healthy and empty cells. Each minute the virus spreads from every infected cell to its healthy neighbours up, down, left and right. Return the number of…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
- Decaying power levels across a graphCodingSome nodes of a graph are power sources with a starting level, and power weakens as it travels along edges. Compute the power level that reaches every node (when several sources…Last asked Feb 2026
- Shortest relationship path between two peopleCodingPeople are linked by relationships (a graph where each edge is a direct relationship). Given two people, return the shortest chain of relationships that connects them, or say that…Last asked Feb 2026
Trapping rain water IICodingGiven a 2D grid of cell heights, compute how much rainwater the grid holds after rain, with water able to run off the outer edge.Last asked Feb 2026- Shortest path between two cells in a gridCodingGiven a grid with open and blocked cells, return the length of the shortest path from a start cell to a target cell moving up, down, left and right. A follow-up changes the…Last asked Feb 2026
- Sliding puzzle: fewest moves to solve the 15-puzzleCodingGiven a 4x4 sliding puzzle with one blank, return the fewest moves to reach the solved board, or report that it cannot be solved. Discuss the solvability check, BFS versus A or…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
- Fewest jumps between two indices of a circular arrayCodingIn a circular array, arri is the exact distance you may jump from index i, either left or right, wrapping around the ends. Given a start index and a target index, return 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
- 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
- Flood fillCodingGiven an image as a grid of colors, a starting pixel and a new color, recolor the starting pixel and every pixel connected to it (up, down, left, right) that has the same original…Last asked Jan 2026
- Distance from every cell to the nearest taxiCodingA grid marks the cells where taxis are parked. Return, for every cell, the distance to the nearest taxi (moving up, down, left or right). Use a multi-source BFS and say why it…Last asked Jan 2026
- Distance from every node to the cycleCodingA connected graph contains exactly one cycle. For every node, return its distance to the nearest node on the cycle. Find the cycle by trimming leaves, then run a multi-source BFS…Last asked Jan 2026
- Walls and gatesCodingA grid holds walls, gates and empty rooms. Fill every empty room with the distance to its nearest gate, leaving rooms that cannot reach a gate untouched. Use one multi-source BFS…Last asked Jan 2026
- Fastest trip when two travellers may meet and ride togetherCodingTwo people start at different nodes of a graph and both need to reach the same destination. They may travel separately, or meet at some node and take the bus together from there…Last asked Jan 2026
- Top K similar movies from a similarity graphCodingMovies are nodes with a rating, and an edge links two similar movies; similarity carries across edges. Given a movie and k, return the k highest-rated movies reachable from it…Last asked Dec 2025
- Word ladderCodingGiven a start word, an end word and a word list, find the length of the shortest sequence from start to end in which each step changes exactly one letter and every word after the…Last asked Dec 2025
- Shortest path in a grid with obstaclesCodingGiven a 2D grid where some cells are blocked, find the length of the shortest path from the top-left cell to the bottom-right cell moving up, down, left or right, or return -1 if…Last asked Dec 2025
- Check completeness of a binary treeCodingGiven the root of a binary tree, return whether it is complete: every level is full except possibly the last, and the nodes on the last level sit as far left as possible. Explain…Last asked Dec 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
- Cells water reaches flowing downhillCodingA 2D map gives the height of each cell. A drop of water lands on one cell and flows to neighbouring cells (up, down, left, right) whose height is not greater than the cell it is…Last asked Oct 2025
Find a way out of a restricted map zoneCodingGiven a starting latitude and longitude and a function that says whether a point is inside a premium zone, return a path that leaves the zone, or a nearby point outside it…Last asked Oct 2025- Find the first error in a log, then trace failures through dependenciesCoding1. A service's log lines are tagged Info, Warn or Error. Once the first Error appears the service is down, so every later line is an Error too, and the line just before the first…Last asked Sep 2025
- Binary tree level order traversalCodingReturn a binary tree's values level by level, each level from left to right, using a queue. Be ready to print each level on its own line or to number the nodes in that order.Last asked Sep 2025
- Shortest path that avoids blocked nodesCodingGiven an unweighted graph, a start node and a set of blocked nodes that cannot be entered, return the shortest distance from the start to every node (or to a given end node), with…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
- 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
- Shortest path in an unweighted graph: BFS versus DFSCodingExplain how to find the shortest path between two nodes of an unweighted graph and its time complexity, without necessarily writing code. Then compare: why breadth-first search…Last asked Sep 2025
- Group movies by graph traversalCodingMovies are linked to each other (for example by shared attributes or similarity pairs). Put every movie into its group, where a group is a set of movies connected through links…Last asked Sep 2025
- Best locker location on a grid with obstaclesCodingOn a grid with obstacles, choose an empty cell for a locker so that the total walking distance to it from a set of given locations is as small as possible, walking around…Last asked Aug 2025
- Shortest path to collect all keysCodingA grid has walls, a start cell, keys (lowercase letters) and locks (the matching uppercase letters). A lock can only be passed once you hold its key. Return the fewest steps to…Last asked Aug 2025
- Reach a destination by bus with limited walkingCodingYou get start and end points on a grid, a walking budget k, and bus routes between pairs of stations, all two-way. Riding a bus costs no walking; walking between points costs…Last asked Aug 2025
- Rotting orangesCodingIn a grid, cells are empty, fresh fruit or rotten fruit. Each minute, fresh fruit next to rotten fruit (up, down, left, right) rots. Return the minutes until no fresh fruit is…Last asked Jul 2025
- Shortest bridgeCodingA grid holds exactly two islands. Return the fewest water cells to flip to connect them: mark one island with depth-first search, then expand from all its cells with breadth-first…Last asked Jul 2025
- Check whether a binary tree is a max-heapCodingDecide whether a binary tree is a valid max-heap: it must be complete (checked level by level) and every node must be at least as large as its children.Last asked Jul 2025
- Same-value region from a start pixel, and its borderCodingAn image is a grid of 0s and 1s. From a starting pixel, find every connected pixel with the same value. Follow-up: return the region's border, the neighbouring pixels that are not…Last asked Jul 2025
- +1Largest island perimeter in a gridCodingYou are given an m x n grid where each cell is either land ("1") or water ("0"). Land cells that touch horizontally or vertically (not diagonally) belong to the same island. Treat…
- Tallest building between parking lotsCodingA city block is drawn as a rectangular grid of strings. Each tile is one of: - 'P': a parking lot. Its height is fixed at 0. - '-': a lot where a building can go. You choose its…
- Type a word on a grid keyboard with a jump limitCodingYou are typing a word with one finger on an unusual keyboard: an m x n grid of characters. Moving the finger from cell (r1, c1) to cell (r2, c2) covers a Manhattan distance of r1…
- Two-colour a board with walls and fixed cellsCodingYou are given an M x N board as a matrix of integers. Each cell is one of: - 1: already painted black - 0: already painted white - 9: empty, still to be painted - -1: a wall…
- Red and black tile slides and jumpsCodingA strip of cells holds red tiles (R), black tiles (B) and empty cells (). The board is a string such as "RRBB". Movement rules - A red tile only moves right. A black tile only…
- Two cars to their destinations without collisionsCodingA parking robot controls two self-driving cars on a rectangular map. The map is a list of equal-length strings. Each character is one cell: - . is road. - is a wall. Cars cannot…
- Connect points that share a row or columnCodingDesign a structure over an unbounded 2D grid. Each cell is either empty or holds a point. You can move from one point to another point in one step when the two points share a row…
- +1Find bottleneck dependencies in a parallel buildCodingYou are given n build targets numbered 0 to n - 1 and a list of directed edges edges. An edge u, v means target v cannot start building until target u has finished. The graph has…