头文件模板

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<string>
#include<cstring>
#include<cmath>
#include<vector>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<time.h>
#define ll long long  
using namespace std;
#define mp make_pair
#define pb push_back
#define lson l,mid,pos<<1
#define rson mid+1,r,pos<<1|1
const double PI=acos(-1); 
const int maxm=2000+5;
const int maxn=5000+5;
const int mod=1e9+7;
const int inf=0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3fLL;
const double eps=1e-8; 
int dir[4][2]={0,1,1,0,0,-1,-1,0};  
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}  
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}  
ll inv(ll b){if(b==1)return 1; return (mod-mod/b)*inv(mod%b)%mod;}  
ll fpow(ll n,ll k){ll r=1;for(;k;k>>=1){if(k&1)r=r*n%mod;n=n*n%mod;}return r;}