记录编号	446458	评测结果	AAAAAAAAAA
题目名称	[HAOI 2015]按位或	最终得分	100
用户昵称	__stdcall	是否通过	通过
代码语言	C++	运行时间	1.680 s
提交时间	2017-09-08 11:45:12	内存使用	8.29 MiB

#include <cstring>
#include <algorithm>
#include <cstdio>
#include <cmath>

using namespace std;
const int MAXN = 20;
const double EPS = 1e-10;
int nowarn;

int dcmp( double x ) {
	if( fabs(x) < EPS ) return 0;
	return x < 0 ? -1 : 1;
}

int n;
double a[1<<MAXN];

bool check() {
	bool vis[MAXN] = {0};
	for( int i = 0; i < (1<<n); ++i )
		if( dcmp( a[i] ) )
			for( int j = 0; j < n; ++j )
				if( i & (1<<j) ) vis[j] = 1;
	for( int i = 0; i < n; ++i )
		if( !vis[i] ) return false;
	return true;
}
void fmt( double *a, int n ) {
	for( int i = 0; i < n; ++i )
		for( int j = 0; j < (1<<n); ++j )
			if( j & (1<<i) )
				a[j] += a[j ^ (1<<i)];
}
void ifmt( double *a, int n ) {
	for( int i = n-1; i >= 0; --i )
		for( int j = (1<<n)-1; j >= 0; --j )
			if( j & (1<<i) )
				a[j] -= a[j ^ (1<<i)];
}

int main() {
	freopen( "haoi2015_set.in", "r", stdin );
	freopen( "haoi2015_set.out", "w", stdout );
	nowarn = scanf( "%d", &n );
	for( int i = 0; i < (1<<n); ++i )
		nowarn = scanf( "%lf", a+i );
	if( !check() ) {
		puts("INF");
		return 0;
	}
	fmt(a, n);
	for( int i = 0; i < (1<<n); ++i ) {
		if( dcmp( a[i] - 1 ) == 0 )
			a[i] = 0;
		else
			a[i] = 1 / ( a[i] - 1 );
	}
	ifmt(a, n);
	printf( "%.10lf\n", a[(1<<n)-1] );
	return 0;
}