rotating the box

https://leetcode.com/problems/rotating-the-box/description/

def rotateTheBox(self, boxGrid: List[List[str]]) -> List[List[str]]:
	rowLength = len(boxGrid)
	colLength = len(boxGrid[0])
 
	# letting the stones fall
	for r in range(rowLength):
		i = colLength - 1
		for c in reversed(range(colLength)):
			# if stone found, replace with empty
			if boxGrid[r][c] == "#":
				boxGrid[r][c],boxGrid[r][i] = boxGrid[r][i], boxGrid[r][c]
				i -= 1
			# if obstacle found, move i pointer next to it
			elif boxGrid[r][c] == "*":
				i = c - 1
					
	# now rotating the boxgrid
	rotatedGrid = []
	rev = boxGrid[::-1]
	for i in range(colLength): # per col
		r = []
		for j in range(rowLength): # per row
			r.append(rev[j][i])
		rotatedGrid.append(r)
	
	return rotatedGrid

trick

1. shift the stones
   • go thru each row, in each row, iterate from the back
   • have 2 pointers: one for tracking the empty space i, one to iterate thru the row c
   • if stone found in c, then swap the position with i then move i
   • if there is an obstacle in c, then the i position is now c + 1 because the rocks now can’t move beyond the obstacle
2. then rotate the box
   • basically the 1st column becomes the 1st row
   • so basically go thru the columns from the bottom