Island Perimeter LeetCode solution in Python

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# Runtime: 382 ms (Top 98.7%) | Memory: 16.57 MB (Top 93.9%)
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class Solution:
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    def islandPerimeter(self, grid: List[List[int]]) -> int:
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        perimeter = 0
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        for i in range(len(grid)):
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            for j in range(len(grid[0])):
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                if grid[i][j] == 1:
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                    perimeter += 4
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                    if i != 0 and grid[i - 1][j] == 1:
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                        perimeter -= 2
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                    if j != 0 and grid[i][j - 1] == 1:
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                        perimeter -= 2
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        return perimeter