CF1749A.Cowardly Rooks

There's a chessboard of size $n \times n$. $m$ rooks are placed on it in such a way that:

• no two rooks occupy the same cell;
• no two rooks attack each other.

A rook attacks all cells that are in its row or column.

Is it possible to move exactly one rook (you can choose which one to move) into a different cell so that no two rooks still attack each other? A rook can move into any cell in its row or column if no other rook stands on its path.

有一个 $n \times n$ 的棋盘。在棋盘上放置了 $m$ 个车（rook），满足以下条件：

• 任意两个车不占据同一格子；
• 任意两个车互不攻击。

一个车会攻击其所在行和列上的所有格子。

是否可能恰好移动一个车（你可以任选其中一个车来移动）到另一个不同的格子，使得移动后仍满足：任意两个车互不攻击？
一个车可以沿其所在行或列移动到任意格子，前提是其路径上没有其他车阻挡。

The first line contains a single integer $t$ ($1 \le t \le 2000$) — the number of testcases.

The first line of each testcase contains two integers $n$ and $m$ ($1 \le n, m \le 8$) — the size of the chessboard and the number of the rooks.

The $i$-th of the next $m$ lines contains two integers $x_i$ and $y_i$ ($1 \le x_i, y_i \le n$) — the position of the $i$-th rook: $x_i$ is the row and $y_i$ is the column.

No two rooks occupy the same cell. No two rooks attack each other.

第一行包含一个整数 $t$（$1 \le t \le 2000$）——测试用例的数量。

每个测试用例的第一行包含两个整数 $n$ 和 $m$（$1 \le n, m \le 8$）——棋盘的大小以及车的数量。

接下来的 $m$ 行中，第 $i$ 行包含两个整数 $x_i$ 和 $y_i$（$1 \le x_i, y_i \le n$）——第 $i$ 辆车的位置：$x_i$ 表示行号，$y_i$ 表示列号。

任意两辆车不占据同一格子，且任意两辆车互不攻击。

For each testcase, print "YES" if it's possible to move exactly one rook into a different cell so that no two rooks still attack each other. Otherwise, print "NO".

对于每个测试用例，如果可以通过恰好移动一个车（rook）到另一个不同的格子，使得任意两个车之间仍然互不攻击，则输出 "YES"；否则输出 "NO"。

In the first testcase, the rooks are in the opposite corners of a $2 \times 2$ board. Each of them has a move into a neighbouring corner, but moving there means getting attacked by another rook.

In the second testcase, there's a single rook in a middle of a $3 \times 3$ board. It has $4$ valid moves, and every move is fine because there's no other rook to attack it.

在第一个测试用例中，车位于 $2 \times 2$ 棋盘的对角角落。每个车均可移动至相邻的角落，但若如此移动，则会被另一辆车攻击。

在第二个测试用例中，一辆车位于 $3 \times 3$ 棋盘的中心。它有 $4$ 种合法移动方式，且每次移动均安全，因为棋盘上没有其他车可攻击它。