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AlgoExpert Remove Islands
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‎README.md

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@@ -866,13 +866,16 @@ First column links to the problem in AlgoExpert, second is the problem's difficu
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| ----------------------------------- | ------------ | --------------------------------------------- |
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| [Insertion Sort][ae&insertion-sort] | 🟢 Easy | [![python](res/py.png)][ae&insertion-sort#py] |
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| [Merge Sort][ae&merge-sort] | 🟣 Very Hard | [![python](res/py.png)][ae&merge-sort#py] |
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| [Remove Islands][ae&remove-islands] | 🟣 Very Hard | [![python](res/py.png)][ae&remove-islands#py] |
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[🔝 Back to Top 🔝](#coding-challenges)
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[ae&insertion-sort]: https://www.algoexpert.io/questions/merge-sort
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[ae&insertion-sort#py]: algoexpert/insertion-sort.py
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[ae&merge-sort]: https://www.algoexpert.io/questions/merge-sort
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[ae&merge-sort#py]: algoexpert/merge-sort.py
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[ae&remove-islands]: https://www.algoexpert.io/questions/remove-islands
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[ae&remove-islands#py]: algoexpert/remove-islands.py
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## HackerRank problems
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‎algoexpert/remove-islands.py

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# Remove Islands
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# 🟠 Medium
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#
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# https://www.algoexpert.io/questions/remove-islands
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#
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# Tags: Array - Matrix - Graph - Depth-First Search
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import timeit
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from typing import List
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# Use depth first search to mark all island cells 4 directionally
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# adjacent to a cell in the edge of the matrix as safe, then visit all
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# cells in the matrix removing any island that has not been marked as
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# safe.
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#
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# Time complexity: O(m*n) - Where m is the number of rows and n is the
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# number of columns.
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# Space complexity: O(1) - The exercise asks us to mutate the input
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# matrix in place, if we didn't want to we could create a copy using
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# O(m*n) memory.
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class Solution:
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def removeIslands(self, matrix: List[List[int]]) -> List[List[int]]:
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NUM_ROWS, NUM_COLS = len(matrix), len(matrix[0])
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# Define a function that turns all 1s of a given island into 2s.
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def dfs(r: int, c: int) -> None:
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# Mark this cell as adjacent to the edge.
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matrix[r][c] = 2
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dir = [[0, 1], [0, -1], [1, 0], [-1, 0]]
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for rc, cc in dir:
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tr = r + rc
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tc = c + cc
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if (
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0 <= tr < NUM_ROWS
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and 0 <= tc < NUM_COLS
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and matrix[tr][tc] == 1
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):
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dfs(tr, tc)
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# Update all 1s adjacent to a border.
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for c in range(NUM_COLS):
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if matrix[0][c]:
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dfs(0, c)
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if matrix[NUM_ROWS - 1][c]:
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dfs(NUM_ROWS - 1, c)
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for r in range(NUM_ROWS):
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if matrix[r][0]:
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dfs(r, 0)
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if matrix[r][NUM_COLS - 1]:
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dfs(r, NUM_COLS - 1)
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# Remove the islands.
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for r in range(NUM_ROWS):
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for c in range(NUM_COLS):
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if matrix[r][c] == 1:
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matrix[r][c] = 0
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elif matrix[r][c] == 2:
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matrix[r][c] = 1
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return matrix
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def test():
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executors = [Solution]
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tests = [
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[[[1]], [[1]]],
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[
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[
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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],
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[
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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[1, 1, 1, 1, 1],
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],
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],
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[
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[
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[1, 0, 0, 0, 0, 0],
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[0, 1, 0, 1, 1, 1],
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[0, 0, 1, 0, 1, 0],
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[1, 1, 0, 0, 1, 0],
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[1, 0, 1, 1, 0, 0],
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[1, 0, 0, 0, 0, 1],
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],
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[
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[1, 0, 0, 0, 0, 0],
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[0, 0, 0, 1, 1, 1],
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[0, 0, 0, 0, 1, 0],
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[1, 1, 0, 0, 1, 0],
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[1, 0, 0, 0, 0, 0],
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[1, 0, 0, 0, 0, 1],
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],
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],
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[
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[
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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],
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[
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
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],
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],
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]
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for executor in executors:
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start = timeit.default_timer()
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for _ in range(1):
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for col, t in enumerate(tests):
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sol = executor()
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result = sol.removeIslands(t[0])
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exp = t[1]
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assert result == exp, (
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f"\033[93m» {result} <> {exp}\033[91m for"
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+ f" test {col} using \033[1m{executor.__name__}"
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)
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stop = timeit.default_timer()
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used = str(round(stop - start, 5))
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cols = "{0:20}{1:10}{2:10}"
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res = cols.format(executor.__name__, used, "seconds")
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print(f"\033[92m» {res}\033[0m")
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test()

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