1859.txt

北大ACM题目例程 详细的解答过程 程序实现 算法分析

#include <stdio.h>
#include <algorithm>

using namespace std;

struct pairs {
	int first, second;
}p[20100];

bool cmp( const pairs& a, const pairs& b ) {
	return a.first<b.first || a.first==b.first&&a.second<b.second;
}

int main( ) {
	int n, i, sx, sy;

	while( true ) {
		scanf( "%d", &n );

		if( n == 0 )
			break;

		sx = sy = 0;
		for( i=0; i<n; i++ ) {
			scanf( "%d%d", &p[i].first, &p[i].second );
			sx += p[i].first;
			sy += p[i].second;
		}
		
		if( ( (n%1) && (sx%n||sy%n) ) || 2*sx%n || 2*sy%n ) {
			printf( "This is a dangerous situation!\n" );
			continue;
		}
		
		stable_sort( p, p+n, cmp );
		
		sx = 2*sx/n; sy = 2*sy/n;
		
		for( i=0; i<=n/2; i++ )
			if( p[i].first+p[n-1-i].first != sx 
				|| p[i].second+p[n-1-i].second != sy )
				break;
			
		if( i > n/2 )
			printf( "V.I.P. should stay at (%.1f,%.1f).\n", sx*0.5, sy*0.5 );
		else
			printf( "This is a dangerous situation!\n" );
	}

	return 0;
}