Add solution for 827-making a large island

Algorithms/Hard/827_MakingALargeIsland/Solution.py

@@ -0,0 +1,101 @@
+class Solution:    
+    ISLAND_MARK = 1
+
+    def _is_in_boundary(self, row_index: int, column_index: int) -> bool:
+        if (row_index < self._row_num and row_index >= 0) and \
+                (column_index < self._column_num and column_index >= 0):
+                return True
+
+        return False
+
+    def _get_island_size(self, 
+                        grid: List[List[int]], 
+                        visited: List[List[int]], 
+                        group_id: int,
+                        row_index: int, 
+                        column_index: int) -> int:        
+        #                 [ up,      down,   left,    right]
+        four_directions = [(0, -1), (0, 1), (-1, 0), (1, 0)]
+
+        queue = []
+        island_size = 1
+
+        queue.append((row_index, column_index))         
+
+        while queue:
+            row_index, column_index = queue.pop(0)             
+            visited[row_index][column_index] = group_id
+
+            for direction in four_directions:       
+                next_row_index = row_index + direction[1]
+                next_col_index = column_index + direction[0]
+
+                if self._is_in_boundary(next_row_index, next_col_index):                    
+                    is_part_island = grid[next_row_index][next_col_index] == Solution.ISLAND_MARK
+                    is_visited = visited[next_row_index][next_col_index] != -1
+
+                    if is_part_island and not is_visited:                        
+                        island_size += 1                        
+                        visited[next_row_index][next_col_index] = group_id
+                        queue.append((next_row_index, next_col_index))
+
+        return island_size
+
+    def _get_max_island_size(self, 
+                            grid: List[List[int]], 
+                            visited: List[List[int]], 
+                            group_id_island_count_map: Dict[int, int], 
+                            row_index: int, 
+                            column_index: int) -> int:
+        #                 [ up,      down,   left,    right]
+        four_directions = [(0, -1), (0, 1), (-1, 0), (1, 0)]
+
+        island_size = 1        
+        group_ids = []
+        for direction in four_directions:       
+            next_row_index = row_index + direction[1]
+            next_col_index = column_index + direction[0]
+
+            if self._is_in_boundary(next_row_index, next_col_index):                    
+                is_part_island = grid[next_row_index][next_col_index] == Solution.ISLAND_MARK
+
+                if is_part_island:
+                    group_id = visited[next_row_index][next_col_index]
+                    group_ids.append(group_id)        
+
+        # using set() to make sure, not to add same group id more than once
+        for group_id in set(group_ids):            
+            island_size += group_id_island_count_map[group_id]        
+
+        return island_size
+
+
+
+    def largestIsland(self, grid: List[List[int]]) -> int:
+        self._row_num = len(grid)
+        self._column_num = len(grid[0])
+
+        visited = [[-1]*self._column_num for _ in range(self._row_num)]
+
+        group_id = 1
+        group_id_island_count_map = {}
+        # will be runnning BFS to explore islands.
+        for row_index in range(self._row_num):
+            for column_index in range(self._column_num):
+                if grid[row_index][column_index] == 1 and visited[row_index][column_index] == -1:                    
+                    island_size = self._get_island_size(grid, visited, group_id, row_index, column_index)
+                    group_id_island_count_map[group_id] = island_size
+                    group_id += 1
+
+        max_island_size = -1
+        # now searching for max island size
+        for row_index in range(self._row_num):
+            for column_index in range(self._column_num):
+                if grid[row_index][column_index] == 0:                                        
+                    max_island_size = max(max_island_size, self._get_max_island_size(grid, visited, group_id_island_count_map, row_index, column_index))
+
+        if max_island_size == -1:
+            # it means there is no zero in the grid, so the whole grid is the island
+            max_island_size = self._row_num * self._column_num
+
+        return max_island_size