01 Matrix LeetCode solution in Python

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class Solution:
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    def updateMatrix(self, mat: List[List[int]]) -> List[List[int]]:
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        if not mat or not mat[0]:
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            return []
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        m, n = len(mat), len(mat[0])
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        queue = deque()
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        MAX_VALUE = m * n
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        # Initialize the queue with all 0s and set cells with 1s to MAX_VALUE.
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        for i in range(m):
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            for j in range(n):
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                if mat[i][j] == 0:
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                    queue.append((i, j))
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                else:
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                    mat[i][j] = MAX_VALUE
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        directions = [(1, 0), (-1, 0), (0, 1), (0, -1)]
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        while queue:
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            row, col = queue.popleft()
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            for dr, dc in directions:
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                r, c = row + dr, col + dc
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                if 0 <= r < m and 0 <= c < n and mat[r][c] > mat[row][col] + 1:
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                    queue.append((r, c))
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                    mat[r][c] = mat[row][col] + 1
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        return mat