Daily hard

Author: Zanger67

my-submissions/h827.md

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+This can basically boil down to an island question where you
+track the sizes of each island and find the cell with the largest sum
+of its NSEW tile sum (North, South, etc.).
+
+Edge case: avoid if an island borders a cell more than once

my-submissions/h827.py

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+# grid value: 0 | 1 ===>>> new grid value: -(island_id)
+class Solution:
+    def largestIsland(self, grid: List[List[int]]) -> int:
+        # Count grid tiles and set the new grid tile to be a negative 
+        # value: the island's assigned ID but negative
+        # This marks islands as visited
+        def propogate_grid(r: int, c: int, grid: List[List[int]], island_id: int) -> int :
+            grid[r][c] = -island_id
+            size = 1
+            if r > 0 and grid[r - 1][c] > 0 :
+                size += propogate_grid(r - 1, c, grid, island_id)
+            if r < len(grid) - 1 and grid[r + 1][c] > 0 :
+                size += propogate_grid(r + 1, c, grid, island_id)
+            if c > 0 and grid[r][c - 1] > 0 :
+                size += propogate_grid(r, c - 1, grid, island_id)
+            if c < len(grid[0]) - 1 and grid[r][c + 1] > 0 :
+                size += propogate_grid(r, c + 1, grid, island_id)
+            return size
+
+        maxx_island = 0
+        island_id_counter = 1
+        island_sizes = {}               # {island_id: size}
+        for r in range(len(grid)) :
+            for c in range(len(grid[0])) :
+                if grid[r][c] > 0 :
+                    island_size = propogate_grid(r, c, grid, island_id_counter)
+                    island_sizes[island_id_counter] = island_size
+                    maxx_island = max(maxx_island, island_size)
+                    island_id_counter += 1
+
+        # If the entire grid is occupied, that's the max size
+        # If not, then we can at least add one tile to the largest
+        # island e.g. if there's only one island
+        if maxx_island == len(grid) * len(grid[0]) :
+            return maxx_island
+        else :
+            maxx_island += 1
+
+        for r in range(len(grid)) :
+            for c in range(len(grid[0])) :
+                if grid[r][c] == 0 :
+                    large_island = 1
+                    ids = set()                         # We don't want to add an island twice
+                    if r > 0 and grid[r - 1][c] :
+                        ids.add(grid[r - 1][c])
+                        large_island += island_sizes[-grid[r - 1][c]]
+                    if r < len(grid) - 1 and grid[r + 1][c] and grid[r + 1][c] not in ids :
+                        ids.add(grid[r + 1][c])
+                        large_island += island_sizes[-grid[r + 1][c]]
+                    if c > 0 and grid[r][c - 1] and grid[r][c - 1] not in ids :
+                        ids.add(grid[r][c - 1])
+                        large_island += island_sizes[-grid[r][c - 1]]
+                    if c < len(grid[0]) - 1 and grid[r][c + 1] and grid[r][c + 1] not in ids :
+                        large_island += island_sizes[-grid[r][c + 1]]
+                    maxx_island = max(maxx_island, large_island)
+
+        return maxx_island