HDU 1796 How many integers can you find

容斥定理：

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<queue>
#include<set>
#include<map>
#include<cstring>
#include<vector>
#include<string>
#define LL long long
using namespace std;
LL num[124],ans;  
LL Gcd( LL a, LL b )
{
   return b == 0 ? a : Gcd( b , a%b ); 
} 
void DFS( LL d , int t , LL lcm ,int cnt , int c )
{
   lcm = num[t]*lcm/Gcd( lcm ,num[t] );
   if( c&1 ) ans += d / lcm;
   else ans -= d / lcm;
   for( int i = t + 1 ; i < cnt ; i ++ )
        DFS( d , i, lcm , cnt , c + 1  );
} 
int main(  )
{
     int  m;LL n; 
     while( scanf( "%I64d %d",&n ,&m )==2 )
     {
           bool flag = 0;
           int cnt = 0;    
           for( int i = 0 ; i < m ; i ++ )
           { 
                scanf( "%I64d",&num[i] );
                if( num[i] != 0 ) num[cnt++] = num[i]; 
           } 
           ans = 0;
           for( int i = 0 ; i < cnt ;i ++ )
           {
                DFS( n-1  , i ,num[i] ,cnt ,1 ); 
           }
           printf( "%I64d\n",ans  );        
     } 
    //system( "pause" );
    return 0;
}