49 lines
1.2 KiB
Python
49 lines
1.2 KiB
Python
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from itertools import product
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'''
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https://leetcode.com/problems/surrounded-regions/discuss/691646/Python-O(mn)-3-colors-dfs-explained
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'''
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board = [
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["X","X","X","X"],
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["X","O","O","X"],
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["X","X","O","X"],
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["X","O","X","X"]
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]
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class Solution:
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def dfs(self, i, j):
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if i<0 or j<0 or i>=self.M or j>=self.N or self.board[i][j] != "O":
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return
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self.board[i][j] = 'T'
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neib_list = [[i+1,j],[i-1,j],[i,j-1],[i,j+1]]
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for x, y in neib_list:
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self.dfs(x, y)
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def solve(self, board):
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if not board: return 0
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self.board, self.M, self.N = board, len(board), len(board[0])
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# run dfs on sides
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for i in range(0, self.M):
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self.dfs(i,0) # left side
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self.dfs(i,self.N-1) # right side
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# run dfs on top and bottom
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for j in range(0, self.N):
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self.dfs(0,j) # top
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self.dfs(self.M-1,j) # bottom
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print(board)
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# itertools.product() is equivalent to nested forloop
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for i,j in product(range(self.M), range(self.N)):
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board[i][j] = "X" if board[i][j] != "T" else "O"
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sol = Solution()
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sol.solve(board)
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print(board)
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