Bomb Enemy — Python

# Time:  O(m * n)
# Space: O(m * n)


class Solution(object):
    def maxKilledEnemies(self, grid):
        """
        :type grid: List[List[str]]
        :rtype: int
        """
        result = 0
        if not grid or not grid[0]:
            return result

        down = [[0 for _ in xrange(len(grid[0]))] for _ in xrange(len(grid))]
        right = [[0 for _ in xrange(len(grid[0]))] for _ in xrange(len(grid))]
        for i in reversed(xrange(len(grid))):
            for j in reversed(xrange(len(grid[0]))):
                if grid[i][j] != 'W':
                    if i + 1 < len(grid):
                        down[i][j] = down[i + 1][j]
                    if j + 1 < len(grid[0]):
                        right[i][j] = right[i][j + 1]
                    if grid[i][j] == 'E':
                        down[i][j] += 1
                        right[i][j] += 1

        up = [0 for _ in xrange(len(grid[0]))]
        for i in xrange(len(grid)):
            left = 0
            for j in xrange(len(grid[0])):
                if grid[i][j] == 'W':
                    up[j], left = 0, 0
                elif grid[i][j] == 'E':
                    up[j] += 1
                    left += 1
                else:
                    result = max(result,
                                 left + up[j] + right[i][j] + down[i][j])

        return result