LeetCode 1091: Shortest Path in Binary Matrix
A clear explanation of finding the shortest path from top-left to bottom-right in a binary matrix using BFS.
Tag
Matrix
100 notes
LeetCode 1074: Number of Submatrices That Sum to Target
A clear explanation of counting submatrices with a given sum using 2D prefix sums combined with the subarray sum equals k technique.
LeetCode 1072: Flip Columns For Maximum Number of Equal Rows
A clear explanation of finding the maximum number of rows that can be made all-equal by flipping columns, using row pattern normalization.
LeetCode 1034: Coloring A Border
A clear explanation of coloring the border of a connected component in a grid using BFS.
LeetCode 1030: Matrix Cells in Distance Order
A clear explanation of sorting matrix cells by Chebyshev distance from a given center cell using BFS.
LeetCode 1020: Number of Enclaves
A clear explanation of counting land cells unreachable from the grid border using BFS from boundary land cells.
LeetCode 944: Delete Columns to Make Sorted
A clear explanation of solving Delete Columns to Make Sorted by checking each column independently.
LeetCode 883: Projection Area of 3D Shapes
A clear explanation of computing the projection areas of stacked cubes from top, front, and side views.
LeetCode 749: Contain Virus
Simulate virus containment by repeatedly quarantining the most dangerous infected region and spreading the remaining regions.
LeetCode 695: Max Area of Island
Find the largest connected island area in a binary grid using depth-first search.
LeetCode 519: Random Flip Matrix
A clear explanation of randomly flipping zero cells in a matrix without repetition using hash mapping and virtual swapping.
LeetCode 505: The Maze II
A clear explanation of finding the shortest rolling distance in a maze using Dijkstra’s algorithm.
LeetCode 419: Battleships in a Board
A clear explanation of counting battleships in a board using one-pass observation without modifying the grid.
LeetCode 305: Number of Islands II
A clear explanation of Number of Islands II using Union-Find to dynamically merge connected land cells.
LeetCode 304: Range Sum Query 2D - Immutable
A clear explanation of Range Sum Query 2D - Immutable using a 2D prefix sum matrix for constant-time rectangle queries.
LeetCode 174: Dungeon Game
A clear explanation of computing the minimum initial health needed to survive a dungeon using reverse dynamic programming.
LeetCode 64: Minimum Path Sum
A clear guide to finding the minimum path sum in a grid using dynamic programming.
LeetCode 63: Unique Paths II
A clear guide to counting unique paths in a grid with obstacles using dynamic programming.
LeetCode 62: Unique Paths
A clear guide to counting unique paths in a grid using dynamic programming.
LeetCode 959: Regions Cut By Slashes
A clear explanation of counting regions formed by slashes using union find over four triangles per cell.
LeetCode 840: Magic Squares In Grid
A clear explanation of the Magic Squares In Grid problem using fixed-size subgrid validation.
LeetCode 835: Image Overlap
A clear explanation of the Image Overlap problem using translation vectors and frequency counting.
LeetCode 832: Flipping an Image
A clear explanation of the Flipping an Image problem using row reversal, bit inversion, and an in-place two-pointer method.
LeetCode 827: Making A Large Island
A clear explanation of the Making A Large Island problem using connected component labeling and island size lookup.
LeetCode 909: Snakes and Ladders
A clear explanation of Snakes and Ladders using breadth-first search over board squares.
LeetCode 892: Surface Area of 3D Shapes
A clear explanation of computing the exposed surface area of stacked cubes by adding tower area and subtracting shared faces.
LeetCode 885: Spiral Matrix III
A clear explanation of generating grid coordinates in an outward clockwise spiral using simulation.
LeetCode 999: Available Captures for Rook
A clear explanation of counting how many pawns a rook can capture by scanning four directions on a chessboard.
LeetCode 994: Rotting Oranges
A clear explanation of finding the minimum time for all oranges to rot using multi-source BFS.
LeetCode 980: Unique Paths III
A clear explanation of counting all paths from start to end that visit every non-obstacle square exactly once using backtracking.
LeetCode 867: Transpose Matrix
A clear explanation of transposing a matrix by swapping row and column indices.
LeetCode 864: Shortest Path to Get All Keys
A clear explanation of finding the minimum moves to collect all keys in a grid using BFS with key bitmasks.
LeetCode 861: Score After Flipping Matrix
A clear explanation of maximizing a binary matrix score using greedy row and column flips.
LeetCode 935: Knight Dialer
A clear explanation of solving Knight Dialer using dynamic programming over the phone keypad graph.
LeetCode 934: Shortest Bridge
A clear explanation of solving Shortest Bridge using DFS to mark one island and BFS to expand toward the other island.
LeetCode 931: Minimum Falling Path Sum
A clear explanation of solving Minimum Falling Path Sum using dynamic programming over matrix rows.
LeetCode 807: Max Increase to Keep City Skyline
A greedy solution for increasing building heights as much as possible while preserving every skyline view.
LeetCode 794: Valid Tic-Tac-Toe State
A clear explanation of validating whether a Tic-Tac-Toe board can occur in a legal game.
LeetCode 782: Transform to Chessboard
A clear explanation of transforming a binary board into a chessboard using feasibility checks and minimum row and column swaps.
LeetCode 778: Swim in Rising Water
A clear explanation of finding the minimum time to reach the bottom-right cell using a priority queue and minimax path reasoning.
LeetCode 773: Sliding Puzzle
A clear explanation of solving the 2 x 3 sliding puzzle using breadth-first search over board states.
LeetCode 766: Toeplitz Matrix
A clear explanation of checking whether every top-left to bottom-right diagonal in a matrix has the same value.
LeetCode 764: Largest Plus Sign
A clear explanation of finding the largest plus sign in a mined grid using four directional dynamic programming scans.
LeetCode 723: Candy Crush
A clear explanation of restoring a Candy Crush board to a stable state using repeated marking, crushing, and gravity simulation.
LeetCode 750: Number Of Corner Rectangles
Count axis-aligned rectangles whose four corners are 1 using column-pair frequency counting.
LeetCode 741: Cherry Pickup
Maximize cherries collected on a round trip by converting the problem into two simultaneous forward paths and solving with dynamic programming.
LeetCode 733: Flood Fill
Recolor the connected component containing the starting pixel using depth-first search.
LeetCode 694: Number of Distinct Islands
Count unique island shapes in a binary grid using DFS and relative coordinates.
LeetCode 675: Cut Off Trees for Golf Event
A clear explanation of cutting trees in increasing height order using repeated BFS on a grid.
LeetCode 661: Image Smoother
A clear explanation of averaging neighboring pixels in a matrix using direct simulation.
LeetCode 655: Print Binary Tree
A clear explanation of formatting a binary tree into a 2D string matrix using tree height and recursive placement.
LeetCode 631: Design Excel Sum Formula
A design solution for a small Excel-like spreadsheet that supports set, get, and dynamic sum formulas.
LeetCode 240: Search a 2D Matrix II
A clear explanation of searching a row-sorted and column-sorted matrix using the top-right corner elimination method.
LeetCode 48: Rotate Image
A clear explanation of Rotate Image using in-place matrix transpose and row reversal.
LeetCode 598: Range Addition II
A clear math solution for counting the maximum values after repeated top-left matrix increment operations.
LeetCode 568: Maximum Vacation Days
A clear explanation of Maximum Vacation Days using dynamic programming over weeks and cities.
LeetCode 566: Reshape the Matrix
A clear explanation of Reshape the Matrix using index mapping from the original matrix to the reshaped matrix.
LeetCode 562: Longest Line of Consecutive One in Matrix
A clear explanation of Longest Line of Consecutive One in Matrix using dynamic programming over four directions.
LeetCode 542: 01 Matrix
A clear explanation of computing the distance to the nearest zero in a binary matrix using multi-source BFS.
LeetCode 533: Lonely Pixel II
A clear explanation of counting black lonely pixels using row counts, column counts, and duplicate row patterns.
LeetCode 531: Lonely Pixel I
A clear explanation of counting black pixels that are alone in both their row and column.
LeetCode 529: Minesweeper
A clear explanation of updating a Minesweeper board using DFS flood fill and adjacent mine counting.
LeetCode 499: The Maze III
A clear explanation of finding the shortest rolling-ball path to the hole using Dijkstra with lexicographic tie-breaking.
LeetCode 498: Diagonal Traverse
A clear explanation of returning matrix elements in diagonal zigzag order by grouping cells with the same row plus column index.
LeetCode 490: The Maze
A clear explanation of deciding whether a rolling ball can stop at the destination using BFS or DFS over stopping cells.
LeetCode 463: Island Perimeter
A clear explanation of counting the perimeter of an island in a grid by adding land-cell edges and subtracting shared edges.
LeetCode 427: Construct Quad Tree
Build a quad tree from a binary square grid using recursive divide and conquer.
LeetCode 422: Valid Word Square
A clear explanation of checking whether rows and columns read the same using direct index comparison.
LeetCode 417: Pacific Atlantic Water Flow
A clear explanation of finding cells that can flow to both oceans using reverse graph traversal from the borders.
LeetCode 407: Trapping Rain Water II
A clear explanation of trapping rain water in a 2D elevation map using a min heap and boundary expansion.
LeetCode 378: Kth Smallest Element in a Sorted Matrix
A clear explanation of finding the kth smallest value in a row-sorted and column-sorted matrix using binary search on values.
LeetCode 363: Max Sum of Rectangle No Larger Than K
A clear explanation of reducing a 2D rectangle problem to a 1D prefix-sum problem with binary search.
LeetCode 361: Bomb Enemy
A clear explanation of finding the best bomb placement in a grid using cached row and column segment counts.
LeetCode 353: Design Snake Game
A clear explanation of implementing Snake Game with a deque for body order and a set for constant-time collision checks.
LeetCode 351: Android Unlock Patterns
A clear explanation of Android Unlock Patterns using backtracking, a jump table, and symmetry optimization.
LeetCode 348: Design Tic-Tac-Toe
A clear explanation of Design Tic-Tac-Toe using row, column, and diagonal counters for constant-time winner checks.
LeetCode 329: Longest Increasing Path in a Matrix
A clear explanation of Longest Increasing Path in a Matrix using DFS with memoization.
LeetCode 317: Shortest Distance from All Buildings
A clear explanation of Shortest Distance from All Buildings using BFS from each building with distance and reach accumulation.
LeetCode 311: Sparse Matrix Multiplication
A clear explanation of Sparse Matrix Multiplication using non-zero entries to avoid wasted work.
LeetCode 308: Range Sum Query 2D - Mutable
A clear explanation of Range Sum Query 2D - Mutable using a 2D Fenwick Tree for efficient updates and rectangle sum queries.
LeetCode 302: Smallest Rectangle Enclosing Black Pixels
A clear explanation of Smallest Rectangle Enclosing Black Pixels using binary search on rows and columns.
LeetCode 296: Best Meeting Point
A median-based solution for minimizing total Manhattan distance in a grid.
LeetCode 289: Game of Life
An in-place matrix simulation for computing the next state of Conway's Game of Life using temporary encoded states.
LeetCode 286: Walls and Gates
A multi-source BFS solution for filling each empty room with its shortest distance to the nearest gate.
LeetCode 221: Maximal Square
A clear explanation of finding the largest square of 1s in a binary matrix using dynamic programming.
LeetCode 212: Word Search II
A clear explanation of finding multiple words in a character board using a Trie and DFS backtracking.
LeetCode 85: Maximal Rectangle
A detailed guide to solving Maximal Rectangle by converting each matrix row into a histogram and applying a monotonic stack.
LeetCode 79: Word Search
A detailed guide to solving Word Search with depth-first search and backtracking on a grid.
LeetCode 200: Number of Islands
A clear explanation of counting connected groups of land cells in a grid using DFS or BFS.
LeetCode 130: Surrounded Regions
Capture surrounded O regions by marking border-connected O cells first, then flipping the remaining O cells.
LeetCode 74: Search a 2D Matrix
A clear guide to searching a sorted 2D matrix using binary search over a virtual one-dimensional array.
LeetCode 73: Set Matrix Zeroes
A clear guide to setting matrix rows and columns to zero in place using the first row and first column as markers.
LeetCode 59: Spiral Matrix II
A clear guide to generating an n x n matrix filled from 1 to n squared in spiral order.
LeetCode 54: Spiral Matrix
A clear guide to reading a matrix in spiral order using shrinking boundaries.
LeetCode 37: Sudoku Solver
A clear explanation of solving a Sudoku board using backtracking and constraint checking.
LeetCode 36: Valid Sudoku
A clear explanation of checking whether a partially filled Sudoku board is valid using hash sets.
Selection in Sorted Matrix
Select the k-th smallest element from a matrix whose rows and columns are sorted.
Sorted Matrix Search
Search a matrix sorted by rows and columns using divide and conquer.
Saddleback Search
Search a matrix sorted by rows and columns using a monotone path from a corner.
Matrix Binary Search
Search a row-major sorted matrix by treating it as a virtual sorted array.