多入口BFS（上下左右）模板

public static void bfs(char[][] grid, boolean[][] visit, int i, int j) {
    Queue<int[]> queue = new LinkedList<int[]>();

    queue.add(new int[] { i, j });

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

    while (queue.size() > 0) {
      int size = queue.size();
      int[] val = queue.poll();

      for (int[] dir : directions) {
        int row = val[0] + dir[0];
        int col = val[1] + dir[1];

        boolean index = (row < grid.length) && (col < grid[0].length) && (row >= 0) && (col >= 0);

        if (index && !visit[row][col] && grid[row][col] == '1') {
          visit[row][col] = true;
          queue.add(new int[] { row, col });
        }
      }
    }

    result += 1;
  }