ZOJ 1041 Transmitters

题意：给你一个能绕圆心转动的半径固定的半圆和N个点，问这个半圆最多能覆盖多少个点，半圆边界上的点也算在覆盖范围内。

首先把半圆半径之外的点全部排除，枚举剩余所有点与圆心的连线。判断在同一侧的点有多少个。

之前忽略的边界情况，WA一次。

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>

const int MAXN = 200;
const double EPS = 1e-9;

struct point
{
    double x, y;
};

point T;
point P[MAXN];
double R;
int N, cnt;

int max( int a, int b )
{
    return a > b ? a : b;
}

double GetDis( point a, point b )
{
    return sqrt( (a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y-b.y) );
}

void GetLine( point a, point b, double& K, double &B )
{
    K = ( a.y - b.y ) / ( a.x - b.x );
    B = a.y - K*a.x;
    return;
}

void solved()
{
    int ans = 0;
    double K, B;
    for ( int i = 0; i < cnt; ++i )
    {
        if ( fabs( P[i].x - T.x ) > EPS )
        {
            GetLine( T, P[i], K, B );
            int count1 = 0;
            int count0 = 0;
            //printf( "K=%f B=%lf\n", K, B );
            for ( int j = 0; j < cnt; ++j )
            {
                //printf("y=%f\n", K * P[j].x - P[j].y + B );
                double temp = K * P[j].x - P[j].y + B;
                if ( temp > 0 ) ++count1;
                else if ( fabs( temp ) < EPS ) ++count0;
            }
            //printf("1=%d 0=%d\n", count1, count0 );
            ans = max( ans, max( cnt - count1, count1 + count0 ) );
        }
        else
        {
            int count1 = 0;
            int count0 = 0;
            for ( int j = 0; j < cnt; ++j )
            {
                if ( P[j].x - T.x > 0 ) ++count1;
                else if ( fabs( P[j].x - T.x ) < EPS ) ++count0;
            }
            //printf("**1=%d 0=%d\n", count1, count0 );
            ans = max( ans, max( cnt - count1, count1 + count0 ) );
        }
    }

    printf("%d\n", ans );
    return;
}

int main()
{
    while ( ~scanf( "%lf%lf%lf", &T.x, &T.y, &R ) )
    {
        if ( R < 0 ) break;
        scanf( "%d", &N );
        cnt = 0;
        for ( int i = 0; i < N; ++i )
        {
            scanf( "%lf%lf", &P[cnt].x, &P[cnt].y );
            double temp = GetDis( T, P[cnt] );
            if ( temp < R || fabs( temp - R ) < EPS ) ++cnt;
        }
        //printf("cnt=%d\n", cnt);

        solved();
    }
    return 0;
}