2017福建省赛Problem B Triangles(判断两三角形位置关系)

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【题目链接】FZU

【题意】给定两个三角形6个点的坐标，判断两个三角形是包含、相交还是相离。

【样例】

【分析】

【代码】

#include<stdio.h>#include<iostream>#include<cmath>using namespace std;int ans;typedef struct{    double x,y;}Point;Point S[6];double area(Point a,Point b,Point c){    double x1,y1,x2,y2,x3,y3;    x1=a.x;x2=b.x;x3=c.x;    y1=a.y;y2=b.y;y3=c.y;    double l1,l2,l3;    l1=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));    l2=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));    l3=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));    if(!l1||!l2||!l3){        return -1;    }    if(l1+l2==l3||l2+l3==l1||l1+l3==l1){        return -1;    }    double cos=(l1*l1+l2*l2-l3*l3)/(2*l1*l2);    double sin=sqrt(1-cos*cos);    double ss=0.5*l1*l2*sin;    return ss;}double mult(Point a, Point b, Point c){return (a.x-c.x)*(b.y-c.y)-(b.x-c.x)*(a.y-c.y);}bool intersect(Point aa, Point bb, Point cc, Point dd){if ( max(aa.x, bb.x)<min(cc.x, dd.x) )return false;if ( max(aa.y, bb.y)<min(cc.y, dd.y) )return false;if ( max(cc.x, dd.x)<min(aa.x, bb.x) )return false;if ( max(cc.y, dd.y)<min(aa.y, bb.y) )return false;if ( mult(cc, bb, aa)*mult(bb, dd, aa)<0 )return false;if ( mult(aa, dd, cc)*mult(dd, bb, cc)<0 )return false;ans++;return true;}int main(){    int T;    bool ins;    cin>>T;    while(T--){        ans=0;        for(int i=0;i<6;i++){            cin>>S[i].x>>S[i].y;        }        intersect(S[0],S[1],S[3],S[4]);        intersect(S[0],S[1],S[3],S[5]);        intersect(S[0],S[1],S[4],S[5]);        intersect(S[0],S[2],S[3],S[4]);        intersect(S[0],S[2],S[3],S[5]);        intersect(S[0],S[2],S[4],S[5]);        intersect(S[1],S[2],S[3],S[4]);        intersect(S[1],S[2],S[3],S[5]);        intersect(S[1],S[2],S[4],S[5]);        //cout<<ans<<endl;        if(!ans){            ins=false;            double s=area(S[0],S[1],S[2]);            for(int i=3;i<6;i++){                double s1=area(S[0],S[1],S[i]);                double s2=area(S[1],S[2],S[i]);                double s3=area(S[0],S[2],S[i]);                if(s1==-1||s2==-1||s3==-1){                    break;                }                if(abs(s1+s2+s3-s)<1e-9)                    ins=true;            }            if(ins)                printf("contain\n");            else                printf("disjoint\n");        }        else            printf("intersect\n");    }    return 0;}

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