The Number of Imposters

Description:

Input:

The first line contains a single integer $$$t$$$ ($$$1 \le t \le 10^4$$$) — the number of test cases. Description of each test case follows.

The first line of each test case contains two integers $$$n$$$ and $$$m$$$ ($$$1 \le n \le 2 \cdot 10^5$$$; $$$0 \le m \le 5 \cdot 10^5$$$) — the number of players except Theofanis and the number of comments.

Each of the next $$$m$$$ lines contains a comment made by the players of the structure "$$$i$$$ $$$j$$$ $$$c$$$" where $$$i$$$ and $$$j$$$ are two distinct integers and $$$c$$$ is a string ($$$1 \le i, j \le n$$$; $$$i \neq j$$$; $$$c$$$ is either imposter or crewmate).

There can be multiple comments for the same pair of $$$(i, j)$$$.

It is guaranteed that the sum of all $$$n$$$ does not exceed $$$2 \cdot 10^5$$$ and the sum of all $$$m$$$ does not exceed $$$5 \cdot 10^5$$$.

Output:

For each test case, print one integer — the maximum possible number of imposters. If the comments contradict each other, print $$$-1$$$.

Sample Input:

5
3 2
1 2 imposter
2 3 crewmate
5 4
1 3 crewmate
2 5 crewmate
2 4 imposter
3 4 imposter
2 2
1 2 imposter
2 1 crewmate
3 5
1 2 imposter
1 2 imposter
3 2 crewmate
3 2 crewmate
1 3 imposter
5 0

Sample Output:

2
4
-1
2
5

Note:

In the first test case, imposters can be Andreas $$$2$$$ and $$$3$$$.

In the second test case, imposters can be Andreas $$$1$$$, $$$2$$$, $$$3$$$ and $$$5$$$.

In the third test case, comments contradict each other. This is because player $$$1$$$ says that player $$$2$$$ is an imposter, and player $$$2$$$ says that player $$$1$$$ is a crewmate. If player $$$1$$$ is a crewmate, then he must be telling the truth, so player $$$2$$$ must be an imposter. But if player $$$2$$$ is an imposter then he must be lying, so player $$$1$$$ can't be a crewmate. Contradiction.