Number of islands

Author: volodimyr

200.number_of_islands/islands.py

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+# 200. Number of islands
+# Topics: 'Array', 'Depth-First Search', 'Breadth-First Search', 'Union Find', 'Matrix'
+# Level: 'Medium'
+
+# Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.
+
+# An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
+
+# Example 1:
+
+# Input: grid = [
+#   ["1","1","1","1","0"],
+#   ["1","1","0","1","0"],
+#   ["1","1","0","0","0"],
+#   ["0","0","0","0","0"]
+# ]
+# Output: 1
+
+# Example 2:
+
+# Input: grid = [
+#   ["1","1","0","0","0"],
+#   ["1","1","0","0","0"],
+#   ["0","0","1","0","0"],
+#   ["0","0","0","1","1"]
+# ]
+# Output: 3
+
+# Constraints:
+
+#     m == grid.length
+#     n == grid[i].length
+#     1 <= m, n <= 300
+#     grid[i][j] is '0' or '1'.
+
+from typing import List
+
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        ROWS, COLS = len(grid), len(grid[0])
+        visited = set()
+    
+        def complete_island(r: int, c: int):
+            if r < 0 or c < 0:
+                return
+            if r == ROWS or c == COLS:
+                return
+            if (r, c) in visited:
+                return
+            if grid[r][c] == '0':
+                return
+            
+            visited.add((r,c))
+            complete_island(r+1, c)
+            complete_island(r-1, c)
+            complete_island(r, c+1)
+            complete_island(r, c-1)
+            
+
+        count = 0
+        for i in range(ROWS):
+            for j in range(COLS):
+                if grid[i][j] == '1' and (i,j) not in visited:
+                    count += 1
+                    complete_island(i, j)
+
+
+        return count

200.number_of_islands/test_islands.py

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+import unittest
+from typing import List
+from islands import Solution
+
+class TestNumIslands(unittest.TestCase):
+    
+    def setUp(self):
+        self.solution = Solution()
+    
+    def test_basic_multiple_islands(self):
+        """Test case with multiple distinct islands"""
+        grid = [
+            ["1","1","1","1","0"],
+            ["1","1","0","1","0"],
+            ["1","1","0","0","0"],
+            ["0","0","0","0","0"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+    
+    def test_separate_islands(self):
+        """Test case with clearly separated islands"""
+        grid = [
+            ["1","1","0","0","0"],
+            ["1","1","0","0","0"],
+            ["0","0","1","0","0"],
+            ["0","0","0","1","1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 3)
+    
+    def test_single_cell_island(self):
+        """Test with single cell island"""
+        grid = [["1"]]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+    
+    def test_single_cell_water(self):
+        """Test with single cell of water"""
+        grid = [["0"]]
+        self.assertEqual(self.solution.numIslands(grid), 0)
+    
+    def test_all_water(self):
+        """Test grid with only water"""
+        grid = [
+            ["0","0","0"],
+            ["0","0","0"],
+            ["0","0","0"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 0)
+    
+    def test_all_land(self):
+        """Test grid with only land (one big island)"""
+        grid = [
+            ["1","1","1"],
+            ["1","1","1"],
+            ["1","1","1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+    
+    def test_diagonal_not_connected(self):
+        """Test that diagonal cells are not considered connected"""
+        grid = [
+            ["1","0","1"],
+            ["0","1","0"],
+            ["1","0","1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 5)
+    
+    def test_complex_shape(self):
+        """Test with complex island shapes"""
+        grid = [
+            ["1","1","0","0","1"],
+            ["1","0","0","1","1"],
+            ["0","0","1","0","0"],
+            ["0","0","0","1","1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 4)
+    
+    def test_snake_island(self):
+        """Test with a snake-like connected island"""
+        grid = [
+            ["1","0","0","0"],
+            ["1","1","0","0"],
+            ["0","1","1","0"],
+            ["0","0","1","1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+    
+    def test_vertical_line(self):
+        """Test with vertical line island"""
+        grid = [
+            ["1"],
+            ["1"],
+            ["1"],
+            ["1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+    
+    def test_horizontal_line(self):
+        """Test with horizontal line island"""
+        grid = [["1","1","1","1"]]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+    
+    def test_checkerboard_pattern(self):
+        """Test with alternating pattern"""
+        grid = [
+            ["1","0","1","0"],
+            ["0","1","0","1"],
+            ["1","0","1","0"],
+            ["0","1","0","1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 8)
+    
+    def test_large_grid_one_island(self):
+        """Test with larger grid containing one island"""
+        grid = [
+            ["1","1","1","1","1"],
+            ["1","0","0","0","1"],
+            ["1","0","0","0","1"],
+            ["1","0","0","0","1"],
+            ["1","1","1","1","1"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+    
+    def test_surrounded_water(self):
+        """Test island surrounded by water"""
+        grid = [
+            ["0","0","0","0","0"],
+            ["0","1","1","1","0"],
+            ["0","1","0","1","0"],
+            ["0","1","1","1","0"],
+            ["0","0","0","0","0"]
+        ]
+        self.assertEqual(self.solution.numIslands(grid), 1)
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)