Grokking #201

class Solution {

  int[][] grid;
  int rows;
  int cols;

  int[][] dirs = new int[][] { {-1, 0}, {0, 1}, {1, 0}, {0, -1} };

  public int closedIsland(int[][] grid) {
    this.grid = grid;
    this.rows = grid.length;
    this.cols = grid[0].length;

    for (int r = 0; r < rows; r++) {
      for (int c = 0; c < cols; c++) {

        // if cell is zero and is at edge, mark it invalid
        if (r == 0 || r == rows - 1 || c == 0 || c == cols - 1) {
          fill(r, c);
        }

      }
    }

    // count number of islands
    int count = 0;
    for (int r = 0; r < rows; r++) {
      for (int c = 0; c < cols; c++) {

        if (grid[r][c] == 0) {
          count++;

          fill(r, c);
        }

      }
    }

    return count;
  }

  void fill(int r, int c) {
    if (r < 0 || r >= rows || c < 0 || c >= cols || grid[r][c] != 0) {
      return;
    }

    grid[r][c] = 1;

    for (int[] dir : dirs) {
      int rr = r + dir[0];
      int cc = c + dir[1];

      fill(rr, cc);
    }
  }
}