Bricks Falling When Hit
You are given an m x n binary grid, where each 1 represents a brick and 0 represents an empty space. A brick is stable if:
- It is directly connected to the top of the grid, or
- At least one other brick in its four adjacent cells is stable.
You are also given an array hits, which is a sequence of erasures we want to apply. Each time we want to erase the brick at the location hits[i] = (rowi, coli). The brick on that location, if it exists, will disappear. Some other bricks may no longer be stable because of that erasure and will fall. Once a brick falls, it is immediately erased from the grid, meaning it does not land on other stable bricks.
Return an array result, where each result[i] is the number of bricks that will fall after the i^th erasure is applied.
Note that an erasure may refer to a location with no brick, and if it does, no bricks drop.
Example 1
1 0 0 0 1 1 1 0
Input
grid = [[1,0,0,0],[1,1,1,0]], hits = [[1,0]]Output
[2]After erasing the brick at (1,0), the two remaining bottom-row bricks are no longer stable and fall, so the result is [2].
Example 2
1 0 0 0 1 1 0 0
Input
grid = [[1,0,0,0],[1,1,0,0]], hits = [[1,1],[1,0]]Output
[0,0]Erasing (1,1) and then (1,0) causes no additional bricks to fall because all remaining bricks after each erasure are stable.
Constraints
- m == grid.length
- n == grid[i].length
- 1 <= m, n <= 200
- grid[i][j] is 0 or 1.
- 1 <= hits.length <= 4 * 10^4
- hits[i].length == 2
- 0 <= xi <= m - 1
- 0 <= yi <= n - 1
- All (xi, yi) are unique.