注意freopen与大样例

#include <bits/stdc++.h>
using namespace std;
#define int long long
int x,y,T;
int gcd(int x,int y)
{
	if(!y)return x;
	return gcd(y,x%y);
}
signed main()
{
	freopen("pigeon.in","r",stdin);
	freopen("pigeon.out","w",stdout);
	cin>>x>>y>>T;
	cout<<T/(x*y/gcd(x,y))<<endl;
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5+5;
int book[N];
int n;
int a[N];
/*
5
2 3 1 4 5
*/
void dfs(int x)
{
	book[x] = 1;
	if(book[a[x]]==0){
		dfs(a[x]);
	}
}
int main()
{
	freopen("permutation.in","r",stdin);
	freopen("permutation.out","w",stdout);
	int T;
	cin>>T;
	while(T--){
		memset(book,0,sizeof(book));
		cin>>n;
		for(int i=1;i<=n;i++)cin>>a[i];
		int res = 0;
		for(int i=1;i<=n;i++){
			if(book[a[i]]==0){
				res++;
				dfs(a[i]);
			}
		}
		cout<<n-res<<endl;	
	}

	return 0;
}

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 2e5+5;
int n,m;
struct node{
	int v,w;
};
vector<node>e[N];
int u[N],v[N],w[N];
int siz[N],res;
void dfs(int x,int fa,int weight)
{
	siz[x] = 1;
	for(int i=0;i<e[x].size();i++){
		int v = e[x][i].v;
		int W = e[x][i].w;
		if(v==fa)continue;
		dfs(v,x,W);
		siz[x]+=siz[v];
	}
	res+=weight*siz[x]*(n-siz[x]);
}
signed main()
{
	freopen("tree.in","r",stdin);
	freopen("tree.out","w",stdout);
	cin>>n>>m;
	for(int i=1;i<n;i++){
		cin>>u[i]>>v[i]>>w[i];
		e[u[i]].push_back({v[i],w[i]});
		e[v[i]].push_back({u[i],w[i]});
	}
	dfs(1,0,0);
	for(int i=1;i<=m;i++){
		int x,y;
		cin>>x>>y;
		int cha = y-w[x];
		w[x] = y;
		int U = u[x],V=v[x];
		if(siz[U]>siz[V])swap(U,V);
		res+=cha*siz[U]*(n-siz[U]);
		cout<<res<<endl;
	}
	
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 5e5+5,Mod=1e9+7;
int n,a[N],cnt[500005],f[500005],B[500005],A[500005];
void init()
{
	f[0] = 1;
	for(int i=1;i<=500000;i++){
		f[i] = (f[i-1]+f[i-1])%Mod;
	}
}
signed main()
{
	freopen("army.in","r",stdin);
	freopen("army.out","w",stdout);
	init();
	cin>>n;
	for(int i=1;i<=n;i++)cin>>a[i],cnt[a[i]]++;
	//cnt[i]i及i的倍数一共有多少人
	for(int i=1;i<=500000;i++){
		for(int j=i+i;j<=500000;j+=i){
			cnt[i]+=cnt[j];
			cnt[i]%=Mod;
		}
	} 
	for(int i=1;i<=500000;i++){
		if(cnt[i]==0)continue;
		B[i] = (cnt[i]*f[cnt[i]-1])%Mod;
	}
	for(int i=500000;i>=1;i--){
		for(int j=i+i;j<=500000;j+=i){
			B[i]-=B[j];
			B[i]%=Mod;
		}
	}
	int res = 0;
	for(int i=2;i<=500000;i++){
		res+=B[i]*i%Mod;
		res%=Mod;
	}
	cout<<res<<endl;
	return 0;
}