Python solution, beats 99.65%


  • 0
    J
    rst = 0
    for g in (grid, zip(*grid)):
        for row in g:
            tmp = 0
            for num in row:
                if num == 1:
                    tmp = 2
                elif tmp == 2 : #  and num == 0
                    rst += 2
                    tmp = 0
            rst += tmp
    return rst
    

    the basic idea is, in one row, every independent island (continuous '1's is one island) has one left side and one right side, then add 2 to the perimeter.

    iterate the grid list from left to right, and top to bottom, then you will get the perimeter.


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