#### 原题说明

On an 8 x 8 chessboard, there is one white rook. There also may be empty squares, white bishops, and black pawns. These are given as characters ‘R’, ‘.’, ‘B’, and ‘p’ respectively. Uppercase characters represent white pieces, and lowercase characters represent black pieces.

The rook moves as in the rules of Chess: it chooses one of four cardinal directions (north, east, west, and south), then moves in that direction until it chooses to stop, reaches the edge of the board, or captures an opposite colored pawn by moving to the same square it occupies. Also, rooks cannot move into the same square as other friendly bishops.

Return the number of pawns the rook can capture in one move.

Example 1:

Input:
`[[".",".",".",".",".",".",".","."],`
`[".",".",".","p",".",".",".","."],`
`[".",".",".","R",".",".",".","p"],`
`[".",".",".",".",".",".",".","."],`
`[".",".",".",".",".",".",".","."],`
`[".",".",".","p",".",".",".","."],`
`[".",".",".",".",".",".",".","."],`
`[".",".",".",".",".",".",".","."]]`
Output: `3`
Explanation:
In this example the rook is able to capture all the pawns.

Example 2:

Input:
`[[".",".",".",".",".",".",".","."],`
`[".","p","p","p","p","p",".","."],`
`[".","p","p","B","p","p",".","."],`
`[".","p","B","R","B","p",".","."],`
`[".","p","p","B","p","p",".","."],`
`[".","p","p","p","p","p",".","."],`
`[".",".",".",".",".",".",".","."],`
`[".",".",".",".",".",".",".","."]]`
Output: `0`
Explanation:
Bishops are blocking the rook to capture any pawn.

Example 3:

Input:
`[[".",".",".",".",".",".",".","."],`
`[".",".",".","p",".",".",".","."],`
`[".",".",".","p",".",".",".","."],`
`["p","p",".","R",".","p","B","."],`
`[".",".",".",".",".",".",".","."],`
`[".",".",".","B",".",".",".","."],`
`[".",".",".","p",".",".",".","."],`
`[".",".",".",".",".",".",".","."]]`
Output: `3`
Explanation:
The rook can capture the pawns at positions `b5`, `d6` and `f5`.

Note:

1. `board.length == board[i].length == 8`
2. `board[i][j]` is either `'R'`, `'.'`, `'B'`, or `'p'`
3. There is exactly one cell with `board[i][j] == 'R'`

#### 解题思路

1) 当遇到边界，则停止当前方向探索
2) 当遇到`'B'`时，则停止当前方向探索
3) 当遇到`'p'`时，`count_p++`并停止当前方向探索
4) 当四个方向均探索完毕，则可以直接返回`count_p`

#### 归纳总结

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