POJ 1556 The Doors

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先算出各点间的直接距离
再用warshall算法求最短路径
#include<stdio.h>#include<string>#include<math.h>#include<iostream>using namespace std;double max(double a,double b) {return a>b?a:b;}double min(double a,double b) {return a<b?a:b;}const double eps = 1e-8;int sgn(double x){if(fabs(x) < eps)return 0;if(x < 0)return -1;else return 1;}struct Point{double x,y;Point(){}Point(double _x,double _y){x = _x;y = _y;}Point operator -(const Point &b)const{return Point(x - b.x,y - b.y);}//叉积double operator ^(const Point &b)const{return x*b.y - y*b.x;}//点积double operator *(const Point &b)const{return x*b.x + y*b.y;}};struct Line{Point s,e;Line(){}//构造函数Line(Point _s,Point _e){s = _s;e = _e;}};//判断线段相交bool inter(Line l1,Line l2){    return         max(l1.s.x,l1.e.x) >= min(l2.s.x,l2.e.x) &&        max(l2.s.x,l2.e.x) >= min(l1.s.x,l1.e.x) &&        max(l1.s.y,l1.e.y) >= min(l2.s.y,l2.e.y) &&        max(l2.s.y,l2.e.y) >= min(l1.s.y,l1.e.y) &&        sgn((l2.s-l1.s)^(l1.e-l1.s))*sgn((l2.e-l1.s)^(l1.e-l1.s)) <= 0 &&        sgn((l1.s-l2.s)^(l2.e-l2.s))*sgn((l1.e-l2.s)^(l2.e-l2.s)) <= 0;}double dist(Point a,Point b){    return sqrt((b-a)*(b-a));}const int MAXN=100;Line line[MAXN];double dis[MAXN][MAXN];const double INF=1e20;int main() {#ifndef ONLINE_JUDGEfreopen("in.txt","r",stdin);#endifint n;double x,y1,y2,y3,y4;while(scanf("%d",&n),n!=-1) {int i,j,k;for(i=1;i<=n;i++) {scanf("%lf%lf%lf%lf%lf",&x,&y1,&y2,&y3,&y4);            line[2*i-1] = Line(Point(x,y1),Point(x,y2));            line[2*i] = Line(Point(x,y3),Point(x,y4));}//确定始点和终点到每个点的距离for(i=0;i<=4*n+1;i++) {for(j=0;j<=4*n+1;j++) {if (i==j) dis[i][j]=0;else dis[i][j]=INF;}}for(i=1;i<=4*n;i++) {int lid=(i+3)/4;bool flag=true;Point tmp;if (i&1) tmp=line[(i+1)/2].s;else tmp=line[(i+1)/2].e;for(int j = 1;j < lid;j++)                if(inter(line[2*j-1],Line(Point(0,5),tmp)) == false                        && inter(line[2*j],Line(Point(0,5),tmp)) == false)                    flag = false;            if(flag)dis[0][i] =dis[i][0] = dist(Point(0,5),tmp);flag=true;for(j=lid+1;j<=n;j++) if (inter(line[2*j-1],Line(Point(10,5),tmp)) == false                        && inter(line[2*j],Line(Point(10,5),tmp)) == false)flag=false;if (flag) dis[i][4*n+1]=dis[4*n+1][i]=dist(Point(10,5),tmp);}//任意两点间距离for(i=1;i<=4*n;i++) {for(j=i+1;j<=4*n;j++) {int lid1=(i+3)/4;int lid2=(j+3)/4;bool flag=true;Point p1,p2;if (i&1) p1=line[(i+1)/2].s;else p1=line[(i+1)/2].e;if (j&1) p2=line[(j+1)/2].s;else p2=line[(j+1)/2].e;for(k=lid1+1;k<lid2;k++) {if (inter(line[2*k-1],Line(p1,p2)) ==false&& inter(line[2*k],Line(p1,p2)) ==false )flag=false;}if (flag) dis[i][j]=dis[j][i]=dist(p1,p2);}}bool flag =true;//始点到终点距离for(i=1;i<=n;i++) {if (inter(line[2*i-1],Line(Point(0,5),Point(10,5))) == false                    && inter(line[2*i],Line(Point(0,5),Point(10,5))) == false)flag=false;}if (flag) dis[0][4*n+1]=dis[4*n+1][0]=10;//warshall算法for(k=0;k<=4*n+1;k++) for(i=0;i<=4*n+1;i++)for(j=0;j<=4*n+1;j++)if (dis[i][k]+dis[k][j]<dis[i][j])dis[i][j]=dis[i][k]+dis[k][j];printf("%.2lf\n",dis[0][4*n+1]);}return 0;}
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