HDU 4629 Burning 几何 + 扫描线

 总体思路参考了 这里。

 细节：1.控制精度，虽然这题没卡精度，不过还是要控制一下。

之前 bool operator<( const Point& A, const Point& B ) 函数没有控制精度，导致了相当大的误差。

2.三点共线的点判掉，虽然不影响结果，但是可以减少点的数目

3.扫入线扫出线的判断：判断第三个点在那两点所形成的的直线的上方还是下方，上方为扫入线, 下方为扫出线

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

using namespace std;

const int MAXN = 20010;

const double eps = 1e-9;

struct Point
{
    double x, y;
    int type;
    Point( double x = 0, double y = 0, int tp = 0 ): x(x), y(y), type(tp) { }
    void read_Point()
    {
        scanf( "%lf%lf", &x, &y );
        return;
    }
};

struct Line
{
    Point a, b;   //线段起点，终点
    int type;     //标记扫入线还是扫出线
    Line() {}
    Line( Point& x, Point& y, int tp ): a(x), b(y), type(tp) {}
};

int cntX;
vector<double> Lx;
vector<Line>   line;
vector<Point>  qujian[MAXN];
double ans[160];

typedef Point Vector;

inline int dcmp( double x )    //控制精度
{
    if ( fabs(x) < eps ) return 0;
    else return x < 0 ? -1 : 1;
}

Vector operator+( Vector A, Vector B )       //向量加
{
    return Vector( A.x + B.x, A.y + B.y );
}

Vector operator-( Vector A, Vector B )       //向量减
{
    return Vector( A.x - B.x, A.y - B.y );
}

Vector operator*( Vector A, double p )      //向量数乘
{
    return Vector( A.x * p, A.y * p );
}

Vector operator/( Vector A, double p )      //向量数除
{
    return Vector( A.x / p, A.y / p );
}

bool operator<( const Point& A, const Point& B )   //两点比较
{
    return dcmp( A.x - B.x ) < 0 || ( dcmp( A.x - B.x ) == 0 && dcmp( A.y - B.y ) < 0 );
}

bool operator==( const Point& a, const Point& b )   //两点相等
{
    return dcmp( a.x - b.x ) == 0 && dcmp( a.y - b.y ) == 0;
}

double Dot( Vector A, Vector B )    //向量点乘
{
    return A.x * B.x + A.y * B.y;
}

double Length( Vector A )           //向量模
{
    return sqrt( Dot( A, A ) );
}

double Angle( Vector A, Vector B )    //向量夹角
{
    return acos( Dot(A, B) / Length(A) / Length(B) );
}

double Cross( Vector A, Vector B )   //向量叉积
{
    return A.x * B.y - A.y * B.x;
}

double Area2( Point A, Point B, Point C )    //向量有向面积
{
    return Cross( B - A, C - A );
}

Vector Rotate( Vector A, double rad )    //向量旋转
{
    return Vector( A.x * cos(rad) - A.y * sin(rad), A.x * sin(rad) + A.y * cos(rad) );
}

Vector Normal( Vector A )    //向量单位法向量
{
    double L = Length(A);
    return Vector( -A.y / L, A.x / L );
}

Point GetLineIntersection( Point P, Vector v, Point Q, Vector w )   //两直线交点
{
    Vector u = P - Q;
    double t = Cross( w, u ) / Cross( v, w );
    return P + v * t;
}

double DistanceToLine( Point P, Point A, Point B )    //点到直线的距离
{
    Vector v1 = B - A, v2 = P - A;
    return fabs( Cross( v1, v2 ) ) / Length(v1);
}

double DistanceToSegment( Point P, Point A, Point B )   //点到线段的距离
{
    if ( A == B ) return Length( P - A );
    Vector v1 = B - A, v2 = P - A, v3 = P - B;
    if ( dcmp( Dot(v1, v2) ) < 0 ) return Length(v2);
    else if ( dcmp( Dot(v1, v3) ) > 0 ) return Length(v3);
    else return fabs( Cross( v1, v2 ) ) / Length(v1);
}

Point GetLineProjection( Point P, Point A, Point B )    // 点在直线上的投影
{
    Vector v = B - A;
    return A + v*( Dot(v, P - A) / Dot( v, v ) );
}

bool SegmentProperIntersection( Point a1, Point a2, Point b1, Point b2 )  //线段相交，交点不在端点
{
    double c1 = Cross( a2 - a1, b1 - a1 ), c2 = Cross( a2 - a1, b2 - a1 ),
                c3 = Cross( b2 - b1, a1 - b1 ), c4 = Cross( b2 - b1, a2 - b1 );
    return dcmp(c1)*dcmp(c2) < 0 && dcmp(c3) * dcmp(c4) < 0;
}

/******************以上模板********************/

int N;

void init()
{
    int len = line.size();
    for ( int i = 0; i < len; ++i )
        for ( int j = i + 1; j < len; ++j )
        {
            //如果线段相交
            if ( SegmentProperIntersection( line[i].a, line[i].b, line[j].a, line[j].b ) )
            {
                //获得交点
                Point pp = GetLineIntersection( line[i].a, line[i].b - line[i].a, line[j].a, line[j].b - line[j].a );
                Lx.push_back( pp.x );
            }
        }

    sort( Lx.begin(), Lx.end() );
    cntX = unique( Lx.begin(), Lx.end() ) - Lx.begin();
    return;
}

void GetAns()
{
    for ( int i = 0; i <= N; ++i ) ans[i] = 0.0;

    for ( int i = 0; i < cntX - 1; ++i )
    {
        int dep = 0;  //覆盖度
        int sz = qujian[i].size();
        double &st = Lx[i], &ed = Lx[i + 1];
        for ( int j = 0; j < sz - 1; ++j )
        {
            dep += qujian[i][j].type;
            ans[dep]+=(ed-st)*(qujian[i][j+1].x-qujian[i][j].x+qujian[i][j+1].y-qujian[i][j].y)/2.0;
        }
    }

    for ( int i = 1; i <= N; ++i )
        printf( "%.10lf
", ans[i] );
    return;
}

//void show()
//{
//    for ( int i = 0; i < cntX - 1; ++i )
//    {
//        int sz = qujian[i].size();
//        for ( int j = 0; j < sz; ++j )
//        {
//            printf( "%.6f %.6f %d
", qujian[i][j].x, qujian[i][j].y, qujian[i][j].type );
//        }
//        puts("******************
");
//    }
//}

void solved()
{
    init();

    for ( int i = 0; i < cntX; ++i ) qujian[i].clear();
    int len = line.size();

    //遍历每个线段
    for ( int i = 0; i < len; ++i )
    {
        //查询线段左端点在Lx的起始位置
        int j = lower_bound( Lx.begin(), Lx.begin() + cntX, line[i].a.x ) - Lx.begin();
        //遍历线段横跨的区间
        for ( ; j < cntX - 1; ++j )
        {
            double st = Lx[j], ed = Lx[j + 1];
            if ( dcmp( line[i].b.x - ed ) < 0 ) break;
            Point p1 = 
　　　　　　　　GetLineIntersection( line[i].a, line[i].b-line[i].a, Point(st,0.0,0), Point(0,1.0,0));
            Point p2 = 
　　　　　　　　GetLineIntersection( line[i].a, line[i].b-line[i].a, Point(ed,0.0,0), Point(0,1.0,0));
            qujian[j].push_back( Point( p1.y, p2.y, line[i].type ) );
        }
    }

    for ( int i = 0; i < cntX - 1; ++i )
        sort( qujian[i].begin(), qujian[i].end() );

    GetAns();
    return;
}

//两点确定直线一般式
void GetABC( Point a, Point b, double& A, double& B, double& C )
{
    if( dcmp( a.x - b.x ) == 0 ) B = 0.0;
    else B = -1.0;
    A = ( b.y - a.y ) / ( b.x - a.x );
    C = a.y - A * a.x;
    return;
}

//判断扫入扫出线
int SaoRuSaoChu( Point p1, Point p2, Point c )
{
    double A, B, C;
    GetABC( p1, p2, A, B, C );
    if ( dcmp( B ) == 0 ) return 0;

    double res = A * c.x + B * c.y + C;
    return dcmp( res ) < 0 ? 1 : -1;  //扫入线 1, 扫出线 -1
}

int main()
{
    //freopen( "1009.in", "r", stdin );
    //freopen( "s.txt", "w", stdout );
    int T;
    scanf( "%d", &T );
    while ( T-- )
    {
        Lx.clear();
        line.clear();
        scanf( "%d", &N );
        for ( int i = 0; i < N; ++i )
        {
            Point p[3];
            for ( int j = 0; j < 3; ++j )
                p[j].read_Point();

            //判断三点共线
            if ( dcmp( Cross( p[1] - p[0], p[2] - p[0] ) == 0 ) ) continue;

            for ( int j = 0; j < 3; ++j )
            {
                Lx.push_back( p[j].x );
                int k = j + 1;
                if ( k >= 3 ) k = 0;
                Line tmpL( p[j], p[k], 0 );
                //令a点为线段左端点, b为线段右端点
                if ( dcmp( tmpL.b.x - tmpL.a.x ) < 0 ) swap( tmpL.a, tmpL.b );

                int m = 3 - j - k;    //除了构成线段的两点外的那个点

                //判断扫入扫出线
                int tp = SaoRuSaoChu( p[j], p[k], p[m] );

                //如果这条线垂直于x轴,既不是扫入也不是扫出线
                if ( tp == 0 ) continue;

                //得到扫入扫出线
                tmpL.type = tp;
                line.push_back( tmpL );
            }
        }

        solved();
        //printf("lineN = %d cntX=%d
", (int)line.size(), (int)Lx.size() );
        //show();
    }
    return 0;
}