Candy Crush — 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;
    }
};