candy-crush.py

# Time:  O((R * C)^2)
# Space: O(1)

# This question is about implementing a basic elimination algorithm for Candy Crush.
#
# Given a 2D integer array board representing the grid of candy,
# different positive integers board[i][j] represent different types of candies.
# A value of board[i][j] = 0 represents that the cell at position (i, j) is empty.
# The given board represents the state of the game following the player's move.
# Now, you need to restore the board to a stable state by crushing candies according to the following rules:
#
# If three or more candies of the same type are adjacent vertically or horizontally,
# "crush" them all at the same time - these positions become empty.
#
# After crushing all candies simultaneously,
# if an empty space on the board has candies on top of itself,
# then these candies will drop until they hit a candy or bottom at the same time.
# (No new candies will drop outside the top boundary.)
#
# After the above steps, there may exist more candies that can be crushed.
# If so, you need to repeat the above steps.
# If there does not exist more candies that can be crushed (ie. the board is stable),
# then return the current board.
# You need to perform the above rules until the board becomes stable, then return the current board.
#
# Example 1:
# Input:
# board = 
# [[110,5,112,113,114],[210,211,5,213,214],[310,311,3,313,314],[410,411,412,5,414],[5,1,512,3,3],[610,4,1,613,614],[710,1,2,713,714],[810,1,2,1,1],[1,1,2,2,2],[4,1,4,4,1014]]
# Output:
# [[0,0,0,0,0],[0,0,0,0,0],[0,0,0,0,0],[110,0,0,0,114],[210,0,0,0,214],[310,0,0,113,314],[410,0,0,213,414],[610,211,112,313,614],[710,311,412,613,714],[810,411,512,713,1014]]

# Note:
# The length of board will be in the range [3, 50].
# The length of board[i] will be in the range [3, 50].
# Each board[i][j] will initially start as an integer in the range [1, 2000].

class Solution(object):
    def candyCrush(self, board):
        """
        :type board: List[List[int]]
        :rtype: List[List[int]]
        """
        R, C = len(board), len(board[0])
        changed = True
        
        while changed:
            changed = False

            for r in xrange(R):
                for c in xrange(C-2):
                    if abs(board[r][c]) == abs(board[r][c+1]) == abs(board[r][c+2]) != 0:
                        board[r][c] = board[r][c+1] = board[r][c+2] = -abs(board[r][c])
                        changed = True

            for r in xrange(R-2):
                for c in xrange(C):
                    if abs(board[r][c]) == abs(board[r+1][c]) == abs(board[r+2][c]) != 0:
                        board[r][c] = board[r+1][c] = board[r+2][c] = -abs(board[r][c])
                        changed = True

            for c in xrange(C):
                i = R-1
                for r in reversed(xrange(R)):
                    if board[r][c] > 0:
                        board[i][c] = board[r][c]
                        i -= 1
                for r in reversed(xrange(i+1)):
                    board[r][c] = 0

        return board