CF1627A.Not Shading

There is a grid with $n$ rows and $m$ columns. Some cells are colored black, and the rest of the cells are colored white.

In one operation, you can select some black cell and do exactly one of the following:

• color all cells in its row black, or
• color all cells in its column black.

You are given two integers $r$ and $c$. Find the minimum number of operations required to make the cell in row $r$ and column $c$ black, or determine that it is impossible.

有一个 $n$ 行 $m$ 列的网格。部分格子被染成黑色，其余格子为白色。

在一次操作中，你可以选择一个黑色格子，并执行以下恰好一种操作：

• 将该格子所在整行的所有格子染成黑色；或
• 将该格子所在整列的所有格子染成黑色。

给定两个整数 $r$ 和 $c$。求使第 $r$ 行第 $c$ 列的格子变为黑色所需的最少操作次数；若不可能实现，请判断并说明。

The input consists of multiple test cases. The first line contains an integer $t$ ($1 \leq t \leq 100$) — the number of test cases. The description of the test cases follows.

The first line of each test case contains four integers $n$, $m$, $r$, and $c$ ($1 \leq n, m \leq 50$; $1 \leq r \leq n$; $1 \leq c \leq m$) — the number of rows and the number of columns in the grid, and the row and column of the cell you need to turn black, respectively.

Then $n$ lines follow, each containing $m$ characters. Each of these characters is either 'B' or 'W' — a black and a white cell, respectively.

输入包含多个测试用例。第一行包含一个整数 $t$（$1 \leq t \leq 100$），表示测试用例的数量。随后是各测试用例的描述。

每个测试用例的第一行包含四个整数 $n$、$m$、$r$ 和 $c$（$1 \leq n, m \leq 50$；$1 \leq r \leq n$；$1 \leq c \leq m$），分别表示网格的行数、列数，以及你需要将其变为黑色的单元格所在的行号和列号。

接下来是 $n$ 行，每行包含 $m$ 个字符。每个字符为 'B' 或 'W'，分别表示黑色单元格和白色单元格。

For each test case, if it is impossible to make the cell in row $r$ and column $c$ black, output $-1$.

Otherwise, output a single integer — the minimum number of operations required to make the cell in row $r$ and column $c$ black.

对于每个测试用例，如果无法将第 $r$ 行第 $c$ 列的单元格变为黑色，则输出 $-1$。

否则，输出一个整数 —— 将第 $r$ 行第 $c$ 列的单元格变为黑色所需的最少操作次数。

The first test case is pictured below.

We can take the black cell in row $1$ and column $2$, and make all cells in its row black. Therefore, the cell in row $1$ and column $4$ will become black.

In the second test case, the cell in row $2$ and column $1$ is already black.

In the third test case, it is impossible to make the cell in row $2$ and column $2$ black.

The fourth test case is pictured below.

We can take the black cell in row $2$ and column $2$ and make its column black.

Then, we can take the black cell in row $1$ and column $2$ and make its row black.

Therefore, the cell in row $1$ and column $1$ will become black.

第一个测试用例如下图所示。

我们可以选取第 $1$ 行第 $2$ 列的黑色格子，并将其所在整行变为黑色。因此，第 $1$ 行第 $4$ 列的格子将变为黑色。

在第二个测试用例中，第 $2$ 行第 $1$ 列的格子原本已是黑色。

在第三个测试用例中，无法使第 $2$ 行第 $2$ 列的格子变为黑色。

第四个测试用例如下图所示。

我们可以选取第 $2$ 行第 $2$ 列的黑色格子，并将其所在整列变为黑色。

接着，我们可以选取第 $1$ 行第 $2$ 列的黑色格子，并将其所在整行变为黑色。

因此，第 $1$ 行第 $1$ 列的格子将变为黑色。