UVAlive 4683 Find The Number

#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <stack>
#include <map>
#include <set>
#include <vector>
#include <sstream>
#include <queue>
#include <utility>
using namespace std;

#define rep(i,j,k) for (int i=j;i<=k;i++)
#define Rrep(i,j,k) for (int i=j;i>=k;i--)

#define Clean(x,y) memset(x,y,sizeof(x))
#define LL long long
#define ULL unsigned long long
#define inf 0x7fffffff
#define mod %100000007

int T;
int p[15];
int m;
LL k;
LL ans;

LL gcd(LL a , LL b)
{
return (a%b==0)?b:gcd(b,a%b);
}

void dfs(int now , int num , LL lcm , LL n)
{
if ( lcm > 1e15 ) return;
if ( num & 1 )
ans+=n/lcm*num;
else ans-=n/lcm*num;
rep(i,now+1,m)
dfs( i , num+1 , lcm/gcd(lcm,p[i])*p[i] , n );
}

int main()
{
cin>>T;
while(T--)
{
scanf("%d %lld",&m,&k);
rep(i,1,m) scanf("%d",p+i);
LL L = 1;
LL R = 1e15;
LL mid;
while(L<R)
{
ans = 0;
mid = (L+R)>>1;
rep(i,1,m)
dfs(i,1,p[i],mid);

if ( ans >= k )
R = mid;
else
L = mid + 1;
}
cout<<L<<endl;
}
return 0;
}