样例过了提交全MLE，救救我

#include<bits/stdc++.h>
using namespace std;
int n,m;
struct DSU
{
	vector<int>f;
	DSU(int n):f(n+1)
	{
		iota(f.begin(),f.end(),0);
	}
	int find(int x)
	{
		return f[x]==x?x:f[x]==find(f[x]);
	}
	bool merge(int a,int b)
	{
		int fa=find(a),fb=find(b);
		if(fa==fb)
			return 0;
		f[fb]=fa;
		return 1;
	}
	bool same(int a,int b)
	{
		return find(a)==find(b);
	}
};
int main()
{
	while(cin>>n)
	{
		if(n==0)
			return 0;
		else
			cin>>m;
		DSU ds(n);
		int a,b,fat=0;
		while(m--)
		{
			cin>>a>>b;
			ds.merge(a,b);
		}
		for(int i=1;i<=n;i++)
			if(ds.find(i)==i)
				fat++;
		
		cout<<fat-1<<"\n";
	}
	return 0;
}