https://h30306.github.io/blog/tags/matrix/Recent content in Matrix onHugo -- gohugo.ioenhwork0511@gmail.com (Wei Yi Chung)hwork0511@gmail.com (Wei Yi Chung)© 2026 Wei Yi ChungWed, 21 Oct 2026 00:00:00 +0000https://h30306.github.io/blog/algorithm/matrix/Wed, 21 Oct 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/algorithm/matrix/Transposing and rotating, converting between 2D indices and a 1D sequence, neighbors and diagonals, and spiral traversal with four boundarieshttps://h30306.github.io/blog/algorithm/bfs/Tue, 20 Oct 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/algorithm/bfs/Connected components, grid flood fill, multi-source BFS, state-space BFS, shortest cycles, and recursion depth in DFShttps://h30306.github.io/blog/leetcode/leetcode-827/Sat, 17 Oct 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-827/LeetCode 827 note: label every island and record its size, then for each 0 add the sizes of the distinct neighboring islands plus 1https://h30306.github.io/blog/leetcode/leetcode-212/Fri, 16 Oct 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-212/LeetCode 212 note: build a Trie of all words, walk it during the grid DFS, remove words once found, and prune empty nodeshttps://h30306.github.io/blog/leetcode/leetcode-2267/Tue, 13 Oct 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-2267/LeetCode 2267 note: the state is (r, c, open balance); the balance can be neither negative nor more than the remaining steps; search the states with BFS / DP and succeed at the end with balance 0https://h30306.github.io/blog/leetcode/leetcode-1210/Sat, 12 Sep 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-1210/LeetCode 1210 note: the BFS state is (tail position, orientation), each move checks its own empty cells, and equal step costs need no heaphttps://h30306.github.io/blog/leetcode/leetcode-4046/Fri, 11 Sep 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-4046/LeetCode 4046 note: Dijkstra with the last direction and the turns used in the state; for the same cell and direction, an earlier pop is cheaper, and if it also used fewer turns it dominates later stateshttps://h30306.github.io/blog/leetcode/leetcode-773/Mon, 07 Sep 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-773/LeetCode 773 note: there are only 6! = 720 boards, so flatten each board into a string as a BFS state, with swaps of 0 and a neighbor as the moveshttps://h30306.github.io/blog/leetcode/leetcode-499/Sun, 06 Sep 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-499/LeetCode 499 note: Dijkstra prioritized by (distance, path string), and the ball stops when it rolls over the holehttps://h30306.github.io/blog/leetcode/leetcode-864/Sat, 05 Sep 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-864/LeetCode 864 note: the BFS state is (position, bitmask of keys), so the same cell with different keys is a different nodehttps://h30306.github.io/blog/leetcode/leetcode-1292/Sun, 30 Aug 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-1292/LeetCode 1292 note: 2D prefix sums plus binary search on the side length; never mix the two binary search styleshttps://h30306.github.io/blog/leetcode/leetcode-2328/Sun, 30 Aug 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-2328/LeetCode 2328 note: strictly increasing means no cycles; dp[cell] = 1 + Σ dp[larger neighbors], processed from largest to smallest value (or by memoized DFS), summed over all cellshttps://h30306.github.io/blog/leetcode/leetcode-2392/Sat, 01 Aug 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-2392/LeetCode 2392 note: row and column conditions are independent, so run one topological sort for each; put x at its row and column positions, and return an empty matrix if either has a cyclehttps://h30306.github.io/blog/leetcode/leetcode-3548/Mon, 27 Jul 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3548/LeetCode 3548 note: try each horizontal cut (transpose for vertical); the difference must equal a cell on the larger side, and a one-row or one-column side can only drop an end cell, while any cell works otherwisehttps://h30306.github.io/blog/leetcode/leetcode-980/Sun, 26 Jul 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-980/LeetCode 980 note: grid backtracking that marks visited cells in place and checks at the end that every empty cell was coveredhttps://h30306.github.io/blog/leetcode/leetcode-3989/Mon, 13 Jul 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3989/LeetCode 3989 note: the kept columns form a subsequence constrained only between neighbors; an LIS-style DP with dp[j] = the longest valid sequence ending at column jhttps://h30306.github.io/blog/leetcode/leetcode-3651/Fri, 26 Jun 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3651/LeetCode 3651 note: compute layer by layer over teleports; arriving at a cell by teleport costs the previous layer’s minimum over cells with value >= it, found with a running minimum after sorting, followed by the usual right / down grid DPhttps://h30306.github.io/blog/leetcode/leetcode-1727/Tue, 23 Jun 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-1727/LeetCode 1727 note: compute each row’s heights of consecutive ones above; columns can be reordered, so sort heights descending and the j-th tallest times j + 1 is a candidatehttps://h30306.github.io/blog/leetcode/leetcode-1878/Tue, 23 Jun 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-1878/LeetCode 1878 note: enumerate every top vertex and size, walk the four edges, and keep the three largest distinct sumshttps://h30306.github.io/blog/leetcode/leetcode-3961/Thu, 18 Jun 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3961/LeetCode 3961 note: every device but one donates its smallest unit to the same device; that device’s rating becomes the global minimum, so pick the one with the smallest second-smallest valuehttps://h30306.github.io/blog/leetcode/leetcode-3905/Sun, 19 Apr 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3905/LeetCode 3905 note: multi-source BFS one layer at a time, collecting the maximum color per cell before writing the layer backhttps://h30306.github.io/blog/leetcode/leetcode-3898/Sun, 12 Apr 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3898/LeetCode 3898 note: the number of ones in row i of the adjacency matrix is vertex i’s degreehttps://h30306.github.io/blog/leetcode/leetcode-1975/Tue, 06 Jan 2026 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-1975/LeetCode 1975 note: minus signs can travel anywhere in pairs but the parity of the negative count never changes; with an odd count, leave one on the smallest absolute valuehttps://h30306.github.io/blog/leetcode/leetcode-3195/Fri, 22 Aug 2025 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3195/LeetCode 3195 note: track the topmost, bottommost, leftmost and rightmost 1; the area is height times widthhttps://h30306.github.io/blog/leetcode/leetcode-3643/Sun, 10 Aug 2025 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3643/LeetCode 3643 note: flip only the submatrix rows, swapping the slices of rows x + i and x + k - 1 - ihttps://h30306.github.io/blog/leetcode/leetcode-1222/Wed, 30 Jul 2025 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-1222/LeetCode 1222 note: step outward from the king in eight directions; the first queen met in each direction can attack, with queens in a set for lookupshttps://h30306.github.io/blog/leetcode/leetcode-3619/Sat, 19 Jul 2025 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3619/LeetCode 3619 note: flood fill each island and sum its values; with up to 10^5 cells, iterate to avoid deep recursionhttps://h30306.github.io/blog/leetcode/leetcode-3070/Sun, 03 Mar 2024 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3070/LeetCode 3070 note: submatrices containing the top-left corner are exactly the 2D prefix sums P[i][j]; count those <= khttps://h30306.github.io/blog/leetcode/leetcode-3071/Sun, 03 Mar 2024 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-3071/LeetCode 3071 note: count each value on and off the Y, enumerate the Y value a and background value b (a != b), and take the fewest cells to changehttps://h30306.github.io/blog/leetcode/leetcode-240/Sat, 12 Nov 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-240/LeetCode 240 note: start at the top-right corner, moving left when larger and down when smaller, eliminating a row or column each stephttps://h30306.github.io/blog/leetcode/leetcode-48/Mon, 31 Oct 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-48/LeetCode 48 note: rotating 90 degrees clockwise is a transpose followed by reversing each row, both in placehttps://h30306.github.io/blog/leetcode/leetcode-417/Sun, 30 Oct 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-417/LeetCode 417 note: walk inward from each ocean’s shore to cells no lower than the current one; cells reached from both oceans are the answerhttps://h30306.github.io/blog/leetcode/leetcode-73/Tue, 25 Oct 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-73/LeetCode 73 note: record which rows and columns contain a 0 first, then update afterward; the follow-up uses the first row and column as markershttps://h30306.github.io/blog/leetcode/leetcode-74/Tue, 25 Oct 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-74/LeetCode 74 note: each row continues the previous one in sorted order, so binary search it as a 1-D array of length m × n, mapping mid to (mid // n, mid % n)https://h30306.github.io/blog/leetcode/leetcode-54/Sat, 22 Oct 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-54/LeetCode 54 note: keep four boundaries and walk right, down, left and up, shrinking a boundary after each sidehttps://h30306.github.io/blog/leetcode/leetcode-59/Sat, 22 Oct 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-59/LeetCode 59 note: keep four boundaries as in LC 54, but fill in 1 to n² instead of readinghttps://h30306.github.io/blog/leetcode/leetcode-36/Fri, 21 Oct 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-36/LeetCode 36 note: each digit may appear once per row, column and 3 × 3 box; put (digit, row), (digit, column) and (digit, box) keys into one sethttps://h30306.github.io/blog/leetcode/leetcode-892/Sat, 24 Sep 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-892/LeetCode 892 note: a stack of v cubes has 4v + 2 faces; subtract 2 × min for each overlap with the stacks above and to the lefthttps://h30306.github.io/blog/leetcode/leetcode-883/Wed, 21 Sep 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-883/LeetCode 883 note: the top view counts nonzero cells, and the front and side views sum each row’s and each column’s maximumhttps://h30306.github.io/blog/leetcode/leetcode-867/Sat, 17 Sep 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-867/LeetCode 867 note: the transpose is n × m with res[j][i] = matrix[i][j]; in Python, zip(*matrix)https://h30306.github.io/blog/leetcode/leetcode-832/Thu, 15 Sep 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-832/LeetCode 832 note: reverse each row and invert its bits, which two pointers can do at oncehttps://h30306.github.io/blog/leetcode/leetcode-766/Tue, 06 Sep 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-766/LeetCode 766 note: every diagonal is constant exactly when each cell equals its upper-left neighborhttps://h30306.github.io/blog/leetcode/leetcode-733/Sat, 03 Sep 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-733/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 equalhttps://h30306.github.io/blog/leetcode/leetcode-661/Mon, 29 Aug 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-661/LeetCode 661 note: each cell becomes the floored average of the existing cells in its 3 × 3 neighborhood, written into a new matrixhttps://h30306.github.io/blog/leetcode/leetcode-566/Sat, 27 Aug 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-566/LeetCode 566 note: return the original if the element counts differ; otherwise element k goes to (k // c, k % c)https://h30306.github.io/blog/leetcode/leetcode-463/Wed, 24 Aug 2022 00:00:00 +0000hwork0511@gmail.com (Wei Yi Chung)https://h30306.github.io/blog/leetcode/leetcode-463/LeetCode 463 note: each land cell contributes 4 edges, minus 2 for each land neighbor above or to the left