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130. Surrounded Regions.cpp
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130. Surrounded Regions.cpp
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// https://leetcode.com/problems/surrounded-regions/
class Solution
{
public:
void solve(vector<vector<char>> &board)
{
markVerticalBoarderRegions(board);
markHorizontalBoarderRegions(board);
flipRegions(board);
}
void flipRegions(vector<vector<char>> &board)
{
for (int i = 0; i < board.size(); ++i)
{
for (int j = 0; j < board[0].size(); ++j)
{
if (board[i][j] == 'W')
board[i][j] = 'O';
else if (board[i][j] == 'O')
board[i][j] = 'X';
}
}
}
void DFS(vector<vector<char>> &board, int i, int j)
{
if (i < 0 || j < 0 || i >= board.size() || j >= board[0].size() || board[i][j] != 'O')
return;
board[i][j] = 'W';
DFS(board, i + 1, j);
DFS(board, i - 1, j);
DFS(board, i, j + 1);
DFS(board, i, j - 1);
}
void markVerticalBoarderRegions(vector<vector<char>> &board)
{
for (int i = 0; i < board.size(); ++i)
{
DFS(board, i, 0);
DFS(board, i, board[0].size() - 1);
}
}
void markHorizontalBoarderRegions(vector<vector<char>> &board)
{
for (int j = 0; j < board[0].size(); ++j)
{
DFS(board, 0, j);
DFS(board, board.size() - 1, j);
}
}
};