【HDOJ】1756 Cupid's Arrow

图论，点在多边形内部的判定。

 /* 1756 */
 #include <iostream>
 #include <string>
 #include <map>
 #include <queue>
 #include <set>
 #include <stack>
 #include <vector>
 #include <deque>
 #include <algorithm>
 #include <cstdio>
 #include <cmath>
 #include <ctime>
 #include <cstring>
 #include <climits>
 #include <cctype>
 #include <cassert>
 #include <functional>
 #include <iterator>
 #include <iomanip>
 using namespace std;
 //#pragma comment(linker,"/STACK:102400000,1024000")

 #define sti                set<int>
 #define stpii            set<pair<int, int> >
 #define mpii            map<int,int>
 #define vi                vector<int>
 #define pii                pair<int,int>
 #define vpii            vector<pair<int,int> >
 #define rep(i, a, n)     for (int i=a;i<n;++i)
 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 #define clr                clear
 #define pb                 push_back
 #define mp                 make_pair
 #define fir                first
 #define sec                second
 #define all(x)             (x).begin(),(x).end()
 #define SZ(x)             ((int)(x).size())
 #define lson            l, mid, rt<<1
 #define rson            mid+1, r, rt<<1|1

 const double eps = 1e-;
 const int maxn = ;

 int dcmp(double x) {
     if (fabs(x) < eps)    return ;
     return x< ? -:;
 }

 typedef struct Point {
     double x, y;

     Point() {}

     Point(double x_, double y_):
         x(x_), y(y_) {}
 } Point;

 Point poly[maxn];
 int n;

 Point operator-(Point A, Point B) {
     return Point(A.x-B.x, A.y-B.y);
 }

 double Dot(Point A, Point B) {
     return A.x*B.x + A.y*B.y;
 }

 double Cross(Point A, Point B) {
     return A.x*B.y - A.y*B.x;
 }

 bool OnSegment(Point P, Point A, Point B) {
     return dcmp(Cross(A-P, B-P))== && dcmp(Dot(A-P, B-P))<=;
 }

 bool isPointInPolygon(Point p, Point *poly) {
     int wn = ;

     rep(i, , n) {
         if (OnSegment(p, poly[i], poly[(i+)%n]))
             return true;
         int k = dcmp(Cross(poly[(i+)%n]-poly[i], p-poly[i]));
         int d1 = dcmp(poly[i].y - p.y);
         int d2 = dcmp(poly[(i+)%n].y - p.y);

         if (k> && d1<= && d2>)    ++wn;
         if (k< && d2<= && d1>)    --wn;
     }

     return wn!=;
 }

 int main() {
     ios::sync_with_stdio(false);
     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     int m;
     bool flag;
     Point p;

     while (scanf("%d",&n) != EOF) {
         rep(i, , n)
             scanf("%lf %lf", &poly[i].x, &poly[i].y);
         scanf("%d", &m);
         while (m--) {
             scanf("%lf %lf", &p.x, &p.y);
             flag = isPointInPolygon(p, poly);
             puts(flag ? "Yes":"No");
         }
     }

     #ifndef ONLINE_JUDGE
         printf("time = %d.\n", (int)clock());
     #endif

     return ;
 }