[UVa]412:Pi

直接硬爆，把所有組合都找出來看看有沒有互質，再求機率即可。

[C](0.108)

	#include<stdio.h>
	#include<math.h>
	int gcd( int a, int b )
	{
	while( (a%=b) && (b%=a) );
	return a+b;
	}
	int main()
	{
	int N;
	while( scanf( "%d", &N ) != EOF && N != 0 )
	{
	int array[100];
	int i;
	for( i = 0 ; i < N ; i++ )
	scanf( "%d", &array[i] );
	int all = ( N * N - N ) / 2;
	int sum = 0;
	int j;
	for( i = 0 ; i < N ; i++ )
	for( j = i+1 ; j < N ; j++ )
	if( gcd( array[i], array[j] ) == 1 )
	sum++;
	if( sum == 0 )
	printf( "No estimate for this data set.\n" );
	else
	{
	printf( "%.6lf\n", sqrt( ((double)all * 6.0) / (double)sum ) );
	}
	}
	return 0;
	}

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