UVA 634 Polygon

判断点是否在多边形内，我的这个模板好久没用了。。。用了下，蛮顺利的。。

 

#include <queue>#include <stack>#include <math.h>#include <stdio.h>#include <stdlib.h>#include <iostream>#include <limits.h>#include <string.h>#include <string>#include <algorithm>using namespace std;const int MAX = 1010;struct point { double x,y;};struct segment{ point a,b;};point p[MAX];const double eps = 1e-6;bool dy(double x,double y){return x > y + eps;}// x > y bool xy(double x,double y){return x < y - eps;}// x < y bool dyd(double x,double y){ return x > y - eps;}// x >= y bool xyd(double x,double y){return x < y + eps;} // x <= y bool dd(double x,double y) {return fabs( x - y ) < eps;} // x == ydouble crossProduct(point a,point b,point c)//向量 ac 在 ab 的方向 {return (c.x - a.x)*(b.y - a.y) - (b.x - a.x)*(c.y - a.y);}bool onSegment(point a, point b, point c){double maxx = max(a.x,b.x);double maxy = max(a.y,b.y);double minx = min(a.x,b.x);double miny = min(a.y,b.y);if( dd(crossProduct(a,b,c),0.0) && dyd(c.x,minx) && xyd(c.x,maxx) && dyd(c.y,miny) && xyd(c.y,maxy) )return true;return false;}point intersection(point u1,point u2,point v1,point v2){point ans = u1;double t = ((u1.x - v1.x)*(v1.y - v2.y) - (u1.y - v1.y)*(v1.x - v2.x))/((u1.x - u2.x)*(v1.y - v2.y) - (u1.y - u2.y)*(v1.x - v2.x));ans.x += (u2.x - u1.x)*t;ans.y += (u2.y - u1.y)*t;return ans;} bool segIntersect(point p1,point p2, point p3, point p4) {double d1 = crossProduct(p3,p4,p1);double d2 = crossProduct(p3,p4,p2);double d3 = crossProduct(p1,p2,p3);double d4 = crossProduct(p1,p2,p4);if( xy(d1 * d2,0.0) && xy(d3 * d4,0.0) )return true;if( dd(d1,0.0) && onSegment(p3,p4,p1) )return true;//如果不判端点相交，则下面这四句话不需要 if( dd(d2,0.0) && onSegment(p3,p4,p2) )return true;if( dd(d3,0.0) && onSegment(p1,p2,p3) )return true;if( dd(d4,0.0) && onSegment(p1,p2,p4) )return true;return false;}bool point_inPolygon(point pot,point p[],int n) {int count = 0;segment l;l.a = pot;l.b.x = 1e10;l.b.y = pot.y;p[n] = p[0];for(int i=0; i<n; i++){if( onSegment(p[i],p[i+1],pot) )return true;if( !dd(p[i].y,p[i+1].y) ){int tmp = -1;if( onSegment(l.a,l.b,p[i]) )tmp = i;elseif( onSegment(l.a,l.b,p[i+1]) )tmp = i+1;if( tmp != -1 && dd(p[tmp].y,max(p[i].y,p[i+1].y)) )count++;elseif( tmp == -1 && segIntersect(p[i],p[i+1],l.a,l.b) )count++;}}if( count % 2 == 1 )return true;return false;}int main(){int n;point pot;while( ~scanf("%d",&n) && n ){for(int i=0; i<n; i++)scanf("%lf%lf",&p[i].x,&p[i].y);scanf("%lf%lf",&pot.x,&pot.y);bool ans = point_inPolygon(pot,p,n);if( ans )printf("T/n");elseprintf("F/n");}return 0;}