"CQ Training Day3" Burning sky

Description

Given a number of triangles, the total area covered by the I triangle is recorded as area (i) region (i), and the output of each of the areas (i) (1<=i<=n) zone (i) (1. Solution

Scan lines.
Sets x that handles the horizontal axis of all vertices and segment intersections first.
Consider the contribution of the graph between X[i] x[i] to x[i+1] x[i+1) to the answer, which can be seen as a trapezoid.
A variable k can be used to record "contribution to area (k) area (k) currently being discussed". You only need to divide the initial input line into two categories: the K+1 and the Out Edge (k-1). Code

#include <iostream> #include <cstdio> #include <algorithm> #include <cstring> #include <
Cmath> #include <cstdlib> using namespace std;
const int MAXN = 50000+5;

Const double EPS = 1e-8;
    int dcmp (double x) {if (Fabs (x) <eps) return 0; Return x>0?
1:-1;
    } struct point{double x, y; Point () {}-(double x,double y): x (x), Y (y) {} bool operator < (const point P) Const {return dcmp (x-p . x) <0| |
    (DCMP (x-p.x) ==0 && dcmp (Y-P.Y) <0);
    } bool operator = = (const point& p) Const {return dcmp (x-p.x) ==0 && dcmp (y-p.y) ==0;
    } void Init () {scanf ("%lf%lf", &x,&y);}
void put () {cout<< "(" <<x<< "," <<y<< ")";}};
typedef point Vector;
Vector operator + (vector a,vector b) {return vector (A.X+B.X,A.Y+B.Y);}
Vector operator-(vector a,vector b) {return vector (A.X-B.X,A.Y-B.Y);}
Vector operator/(vector v,double t) {return vector (v.x/t,v.y/t);} Vector opErator * (vector v,double t) {return vector (v.x*t,v.y*t);} double Cross (vector a,vector b) {return a.x*b.y-a.y*b.x;}

BOOL Onleft (point A1,point a2,point p) {return cross (P-A1,A2-A1) <0;}
    BOOL Intersect (Point a1,point a2,point b1,point B2) {Double C1 = Cross (A2-A1,B1-A1), C2 = Cross (A2-A1,B2-A1);
    Double C3 = Cross (B2-B1,A1-B1), C4 = Cross (B2-B1,A2-B1); 
Return dcmp (C1) *dcmp (C2) <0 &&dcmp (C3) *dcmp (C4) <0;
    } point intersection (Point A1,point a2,point b1,point b2) {Vector V1 = A2-a1,v2 = B2-B1;
    Double T = Cross (B1-A1,V2)/cross (V1,V2);
return a1+v1*t;
    } struct seg{point a1,a2;
    int type;
        SEG () {} seg (point a1,point a2,int Type): A1 (A1), A2 (A2), type (type) {} BOOL operator < (const SEG s) Const { Return dcmp (a1.y-s.a1.y) ==-1 | |
    (DCMP (A1.Y-S.A1.Y) ==0 && dcmp (A2.Y-S.A2.Y) ==-1);

}}Q[MAXN],A[MAXN];
int N,n,tot;

Double X[MAXN],ANS[MAXN];
    int main () {int i,j,k;
    scanf ("%d", &n); for (i=1;i<=n;i++){Point p[3];
        for (j=0;j<3;j++) P[j].init (), x[++tot] = p[j].x;
        if (Cross (p[0]-p[1],p[0]-p[2]) ==0) continue;
            for (k=2,j=0;j<3;k=j++) {Point A = P[k],b = P[j];
            if (dcmp (a.x-b.x) ==0) continue;
            if (b<a) swap (A, b);
            Point C = p[3-j-k];
            if (Onleft (a,b,c)) a[++n] = Seg (a,b,1);
        else A[++n] = Seg (a,b,-1); }} for (i=1;i<=n;i++) for (j=i+1;j<=n;j++) if (Intersect (A[I].A1,A[I].A2,A[J].A1,A[J].A2)
                ) {Point temp = intersection (A[I].A1,A[I].A2,A[J].A1,A[J].A2);
            X[++tot] = temp.x;
    } sort (X+1,x+1+tot); int t = 0;
    X[0] =-1;
    for (i=1;i<=tot;i++) if (dcmp (x[i]-x[t))!=0) x[++t] = X[i];
    tot = t;
        for (i=1;i<tot;i++) {int top = 0; for (j=1;j<=n;j++) if (A[j].a1.x<=x[i] && a[j].a2.x>=x[i+1]) {Point L = interse Ction (A[j].A1,a[j].a2,point (x[i],-1000), point (x[i],1000));
                Point r = Intersection (A[j].a1,a[j].a2,point (x[i+1],-1000), point (x[i+1],1000));
            Q[++top] = Seg (L,r,a[j].type);
        } sort (q+1,q+1+top);
        k = 0;
            for (j=1;j<top;j++) {k + = Q[j].type;
            Double area = ((Q[J+1].A1.Y-Q[J].A1.Y) + (Q[J+1].A2.Y-Q[J].A2.Y)) * (X[i+1]-x[i]) *0.5;
        Ans[k] + = area;
    }} for (i=1;i<=n;i++) printf ("%.4lf\n", Ans[i]);
return 0; }