Leetcode#130 Surrounded Regions

 1 void replace(vector<vector<char> > &board, int i, int j, char before, char after) {
 2   stack<pair<int, int> > st;
 3   int rlen = board.size();
 4   int clen = board[0].size();
 5   int rnext[4] = {-1, 1, 0, 0};
 6   int cnext[4] = {0, 0, -1, 1};
 7 
 8   st.push(pair<int, int>(i, j));
 9   while (!st.empty()) {
10     pair<int, int> top = st.top();
11     st.pop();
12     if (top.first < 0 || top.first >= rlen || top.second < 0 || top.second >= clen || board[top.first][top.second] != before)
13       continue;
14     board[top.first][top.second] = after;
15     for (int k = 0; k < 4; k++)
16       st.push(pair<int, int>(top.first + rnext[k], top.second + cnext[k]));
17   }
18 }
19 
20 void solve(vector<vector<char>> &board) {
21   if (board.empty() || board[0].empty()) return;
22   int rlen = board.size();
23   int clen = board[0].size();
24 
25   for (int i = 0; i < rlen; i++) {
26     replace(board, i, 0, ‘O‘, ‘#‘);
27     replace(board, i, clen - 1, ‘O‘, ‘#‘);
28   }
29   for (int j = 0; j < clen; j++) {
30     replace(board, 0, j, ‘O‘, ‘#‘);
31     replace(board, rlen - 1, j, ‘O‘, ‘#‘);
32   }
33 
34   for (int i = 1; i < rlen - 1; i++)
35     for (int j = 1; j < clen - 1; j++)
36       if (board[i][j] == ‘O‘)
37         board[i][j] = ‘X‘;
38 
39   for (int i = 0; i < rlen; i++) {
40     replace(board, i, 0, ‘#‘, ‘O‘);
41     replace(board, i, clen - 1, ‘#‘, ‘O‘);
42   }
43   for (int j = 0; j < clen; j++) {
44     replace(board, 0, j, ‘#‘, ‘O‘);
45     replace(board, rlen - 1, j, ‘#‘, ‘O‘);
46   }
47 }