[Leetcode] 723. Candy Crush

This question is about implementing a basic elimination algorithm for Candy Crush.

Given a 2D integer ArrayboardRepresenting the grid of candy, different positive integersboard[i][j]Represent different types of candies. A valueboard[i][j] = 0Represents 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 toStable StateBy crushing candies according to the following rules:

1. 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.
2. 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 .)
3. After the above steps, there may exist more candies that can be crushed. If so, you need to repeat the above steps.
4. If there does not exist more candies that can be crushed (ie. The board isStable), 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]]Explanation: 

 

Note:

1. The lengthboardWill be in the range [3, 50].
2. The lengthboard[i]Will be in the range [3, 50].
3. Eachboard[i][j]Will initially start as an integer in the range [1, 2000].

A two-dimensional array board is given to a question similar to the candy elimination game. The array represents candy and three or more consecutive identical numbers can be eliminated in the horizontal and vertical directions, after elimination, the number at the top fills in the space. Note that the candy that can be eliminated will be removed and then dropped for the second elimination. It remains stable until it is eliminated.

Solution: Mark all elements to be crush ed, remove these elements, and then drop the number above and change the vacancy to 0. The difficulty is how to determine which elements need to be crush.

Python:

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　

C ++:

// Time:  O((R * C)^2)// Space: O(1)class Solution {public:    vector<vector<int>> candyCrush(vector<vector<int>>& board) {        const auto R = board.size(), C = board[0].size();        bool changed = true;                while (changed) {            changed = false;                        for (int r = 0; r < R; ++r) {                for (int c = 0; c + 2 < C; ++c) {                    auto v = abs(board[r][c]);                    if (v != 0 && v == abs(board[r][c + 1]) && v == abs(board[r][c + 2])) {                        board[r][c] = board[r][c + 1] = board[r][c + 2] = -v;                        changed = true;                    }                }            }                        for (int r = 0; r + 2 < R; ++r) {                for (int c = 0; c < C; ++c) {                    auto v = abs(board[r][c]);                    if (v != 0 && v == abs(board[r + 1][c]) && v == abs(board[r + 2][c])) {                        board[r][c] = board[r + 1][c] = board[r + 2][c] = -v;                        changed = true;                    }                }            }            for (int c = 0; c < C; ++c) {                int empty_r = R - 1;                for (int r = R - 1; r >= 0; --r) {                    if (board[r][c] > 0) {                        board[empty_r--][c] = board[r][c];                    }                }                for (int r = empty_r; r >= 0; --r) {                    board[r][c] = 0;                }            }        }                return board;    }};　　

C ++:

class Solution {public:    vector<vector<int>> candyCrush(vector<vector<int>>& board) {        int m = board.size(), n = board[0].size();        while (true) {            vector<pair<int, int>> del;            for (int i = 0; i < m; ++i) {                for (int j = 0; j < n; ++j) {                    if (board[i][j] == 0) continue;                    int x0 = i, x1 = i, y0 = j, y1 = j;                    while (x0 >= 0 && x0 > i - 3 && board[x0][j] == board[i][j]) --x0;                    while (x1 < m && x1 < i + 3 && board[x1][j] == board[i][j]) ++x1;                    while (y0 >= 0 && y0 > j - 3 && board[i][y0] == board[i][j]) --y0;                    while (y1 < n && y1 < j + 3 && board[i][y1] == board[i][j]) ++y1;                    if (x1 - x0 > 3 || y1 - y0 > 3) del.push_back({i, j});                }            }            if (del.empty()) break;            for (auto a : del) board[a.first][a.second] = 0;            for (int j = 0; j < n; ++j) {                int t = m - 1;                for (int i = m - 1; i >= 0; --i) {                    if (board[i][j]) swap(board[t--][j], board[i][j]);                   }            }        }        return board;    }};

C ++:

class Solution {public:    vector<vector<int>> candyCrush(vector<vector<int>>& board) {        int m = board.size(), n = board[0].size();        bool toBeContinued = false;                for (int i = 0; i < m; ++i) { // horizontal crushing             for (int j = 0; j + 2 < n; ++j) {                int& v1 = board[i][j];                int& v2 = board[i][j+1];                int& v3 = board[i][j+2];                                int v0 = std::abs(v1);                                if (v0 && v0 == std::abs(v2) && v0 == std::abs(v3)) {                    v1 = v2 = v3 = - v0;                    toBeContinued =  true;                }            }        }                for (int i = 0; i + 2 < m; ++i) {  // vertical crushing            for (int j = 0; j < n; ++j) {                int& v1 = board[i][j];                int& v2 = board[i+1][j];                int& v3 = board[i+2][j];                int v0 = std::abs(v1);                if (v0 && v0 == std::abs(v2) && v0 == std::abs(v3)) {                    v1 = v2 = v3 = -v0;                    toBeContinued = true;                }            }        }                for (int j = 0; j < n; ++j) { // gravity step            int dropTo = m - 1;            for (int i = m - 1; i >= 0; --i) {                if (board[i][j] >= 0) {                    board[dropTo--][j] = board[i][j];                }            }                        for (int i = dropTo; i >= 0; i--) {                board[i][j] = 0;            }        }                return toBeContinued ? candyCrush(board) : board;            }};

　　

　　

 

[Leetcode] 723. Candy Crush