Content: bedbugs are crazy

Professor hope studies the sexual orientation of bedbugs. Before the experiment, he figured out the sex of n bedbugs and marked the number on their backs
Word number (1-N). Now pair a batch of bedbugs to see if they are gay.
Input description
The first line is the integer C, followed by c test cases.
The first line of each test case is the number of bedbugs n (12000), and the number of pairs m (110 ^ 6). Next
The row of is the number of m pairs of bedbugs
Output description
There are c lines in total, and each line prints "testcase i: no homosexuality found", or "testcase i: homosexuality found"
sample input
2
3 3
1 2
2 3
1 3
4 2
1 2
3 4

sample output

testcase 1: Discovering homosexuality
testcase 2: no homosexuality found
It took me a long time, and the simple application of the search set should be, but it still went around, and the search set should make the same sex become a group, so we should open an array to store its objects, and finally we can't use cin, cout, change to c to be able to pass the school oj

#include<iostream> 
#include<cstdio>
#include<vector>
#include<cstring>	
#define lowbit(x) ((x)&(-x))
#define maxn 100005
using namespace std;

int pre[100000];
int l[100000];//For storing objects
int t, n, m;
void init(int a)
{
	for (int i = 1; i <= a; i++)
		pre[i] = i;
}

int find(int a)
{
	if (pre[a] == a)
		return a;
	return pre[a] = find(pre[a]);
}

void unit(int a, int b)
{
	if (find(a) != find(b))
		pre[a] = b;
}

int main()
{
	scanf("%d", &t);
	int k = 0;
	while (t--)
	{
		scanf("%d %d", &n, &m);
		init(n);
		int a, b;
		bool flag = false;
		for (int i = 0; i < m; i++)
		{
			scanf("%d %d", &a, &b);
			if (flag) continue;
			if (!l[a] && !l[b])
			{
				l[a] = b;
				l[b] = a;
			}
			else if (l[a] && !l[b]) l[b] = a, unit(b, l[a]);//If two bedbugs have no objects, they are opposite to each other
			else if (!l[a] && l[b]) l[a] = b, unit(a, l[b]);//If one of them has an object, then the new object and the original one are the same sex. It is necessary to merge and query the set
			else unit(l[a], b), unit(a, l[b]);
			if (find(a) == find(b)) flag = true;
		}
		printf("testcase %d:", ++k);
		if (flag)
			printf("Discovery of homosexuality\n");
		else
			printf("No homosexuality found\n");
	}
}