Practice/Snowflake/Leetcode 1861. Rotating the Box

Leetcode 1861. Rotating the Box

CodingOptional

Problem

You are given a 2D grid representing a box view from the side. The grid contains three types of elements:

• '#' represents a movable block
• '*' represents a fixed obstacle
• '.' represents an empty space

Your task is to:

1. Rotate the entire grid 90 degrees clockwise
2. Apply gravity so that all movable blocks fall downward until they hit either an obstacle, another block, or the bottom of the grid

Return the resulting grid after both transformations.

Requirements

1. First, perform a 90-degree clockwise rotation on the grid
2. Then simulate gravity pulling all blocks ('#') downward
3. Obstacles ('*') remain fixed and block falling blocks
4. Blocks stack on top of each other and cannot pass through obstacles
5. Empty spaces ('.') allow blocks to fall through

Constraints

• 1 <= m, n <= 100 where m is the number of rows and n is the number of columns
• The grid contains only the characters '#', '*', and '.'
• After rotation, the grid dimensions become n × m
• Time complexity should be O(m × n)
• Space complexity should be O(m × n) for the result grid

Examples

Example 1:

` Input: grid = [['#', '.', '*'], ['.', '#', '.'], ['#', '#', '.']]

Output: [['.', '#', '#'], ['#', '.', '#'], ['*', '.', '.']]

Explanation: Step 1 - Original grid:

. *

. # .

# .

Step 2 - After 90° clockwise rotation:

.

# .

. . *

Step 3 - After applying gravity (blocks fall down): . # #

.

• . . `

Example 2:

` Input: grid = [['#', '#', '.', '.', '#']]

Output: [['.'], ['.'], ['#'], ['#'], ['#']]

Explanation: After rotation, all three blocks fall to the bottom. `

Example 3:

` Input: grid = [['#', '.', '#'], ['', '', '*'], ['#', '.', '.']]

Output: [['#', '', '#'], ['.', '', '.'], ['#', '*', '.']]

Explanation: The middle row of obstacles prevents blocks from falling through. `