Leetcode#130 Surrounded Regions

原题地址

1. 把所有与边界联通的"O"替换成别的字符，比如"#"

2. 把剩下的所有"O"替换成"X"

3. 把所有与边界联通的"#"替换成"X"

代码：

void replace(vector<vector<char> > &board, int i, int j, char before, char after) {
  stack<pair<int, int> > st;
  int rlen = board.size();
  int clen = board[0].size();
  int rnext[4] = {-1, 1, 0, 0};
  int cnext[4] = {0, 0, -1, 1};

  st.push(pair<int, int>(i, j));
  while (!st.empty()) {
    pair<int, int> top = st.top();
    st.pop();
    if (top.first < 0 || top.first >= rlen || top.second < 0 || top.second >= clen || board[top.first][top.second] != before)
      continue;
    board[top.first][top.second] = after;
    for (int k = 0; k < 4; k++)
      st.push(pair<int, int>(top.first + rnext[k], top.second + cnext[k]));
  }
}

void solve(vector<vector<char>> &board) {
  if (board.empty() || board[0].empty()) return;
  int rlen = board.size();
  int clen = board[0].size();

  for (int i = 0; i < rlen; i++) {
    replace(board, i, 0, 'O', '#');
    replace(board, i, clen - 1, 'O', '#');
  }
  for (int j = 0; j < clen; j++) {
    replace(board, 0, j, 'O', '#');
    replace(board, rlen - 1, j, 'O', '#');
  }

  for (int i = 1; i < rlen - 1; i++)
    for (int j = 1; j < clen - 1; j++)
      if (board[i][j] == 'O')
        board[i][j] = 'X';

  for (int i = 0; i < rlen; i++) {
    replace(board, i, 0, '#', 'O');
    replace(board, i, clen - 1, '#', 'O');
  }
  for (int j = 0; j < clen; j++) {
    replace(board, 0, j, '#', 'O');
    replace(board, rlen - 1, j, '#', 'O');
  }
}

一开始是用递归去替换，结果爆栈了（Runtime error），只好老老实实用栈。。