题解

#include <bits/stdc++.h>

using namespace std;

int n, k;
const int MAX_ROWS = 100;
const int MAX_COLS = 10;
vector<vector<char>> board(MAX_ROWS, vector<char>(MAX_COLS));
vector<vector<bool>> visited(MAX_ROWS, vector<bool>(MAX_COLS));
vector<pair<int, int>> component;
int floodfill(int i, int j, char color) {
	int cnt = 1;
	if (i < 0 || j < 0 || i >= n || j >= MAX_COLS || visited[i][j] ||
	    board[i][j] != color) {
		return 0;
	}

	visited[i][j] = 1;
	component.push_back({i, j});
	cnt += (floodfill(i + 1, j, color) + floodfill(i - 1, j, color) +
	        floodfill(i, j + 1, color) + floodfill(i, j - 1, color));
	return cnt;
}

int main() {
	cin >> n >> k;

	for (int i = n - 1; i >= 0; i--) {
		string nums;
		cin >> nums;
		for (int j = 0; j < MAX_COLS; j++) { board[i][j] = nums[j]; }
	}
	bool board_changed = true;
	while (board_changed) {
		board_changed = false;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < MAX_COLS; j++) {
				if (!visited[i][j] && board[i][j] != '0') {
					char current_color = board[i][j];
					int cnt = floodfill(i, j, current_color);

					if (cnt >= k) {
						// found a region to destroy
						board_changed = true;
						for (auto p : component) {
							board[p.first][p.second] = '0';
						}
					}
					component.clear();
				}
			}
		}
		for (int col = 0; col < MAX_COLS; col++) {
			vector<char> column_after_gravity;
			for (int row = 0; row < n; row++) {
				if (board[row][col] != '0') {
					column_after_gravity.push_back(board[row][col]);
				}
			}
			for (int row = 0; row < n; row++) {
				if (row < column_after_gravity.size()) {
					board[row][col] = column_after_gravity[row];
				} else {
					board[row][col] = '0';
				}
			}
		}
		fill(visited.begin(), visited.end(), vector<bool>(MAX_COLS, false));
	}

	for (int i = n - 1; i >= 0; i--) {
		for (int j = 0; j < MAX_COLS; j++) { cout << board[i][j]; }
		cout << '\n';
	}
}