skyline1.py

class Solution:
    def getSkyline(self, buildings: List[List[int]]) -> List[List[int]]: 
        
        def divide_conquer(i, j): 
            if j < i:
                return []
            elif j == i:
                x1, x2, h = buildings[i]
                return [[x1, h], [x2, 0]]
            else:                 
                middle = (i + j) // 2
                part1 = divide_conquer(i, middle)
                part2 = divide_conquer(middle + 1, j)
                # merge 
                i, j = 0, 0
                y1, y2 = 0, 0 
                result = []
                old_y = None
                while i < len(part1) and j < len(part2):
                    xi, yi = part1[i]
                    xj, yj = part2[j] 
                    if xi <= xj:
                        new_x = xi                                            
                        y1 = yi
                        i += 1
                    if xj <= xi:
                        new_x = xj
                        y2 = yj
                        j += 1
                        
                    new_y = max(y1, y2)
                    if old_y != new_y:
                        result.append([new_x, new_y]) 
                        old_y = new_y
                return result + part1[i:] + part2[j:]
        
        
        return divide_conquer(0, len(buildings) - 1)