ZOJ1081 Points Within

PS: 判断点是否在多边形内，用的绕圈法，具体参见刘汝佳的训练指南。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>
using namespace std;

struct point {
    int x, y;
    point(double x=0, double y=0):x(x),y(y) {}
};
point operator - (point A, point B) {
    return point(A.x-B.x, A.y-B.y);
}

double Cross(point A, point B) {
    return A.x*B.y - A.y*B.x;
}
vector<point> v;
vector<point> Contain;
vector<point> check;
int n, m;
const double eps = 1e-10;
int dcmp(double x) {
    if(fabs(x)<eps) return 0;
    else return x < 0 ? -1 : 1;
}

double Dot(point a, point b) {
    return a.x*b.x + a.y*b.y;
}
bool OnSegment(point p, point a1, point a2) {
    return dcmp(Cross(a1-p, a2-p))==0 && dcmp(Dot(a1-p, a2-p))<=0;
}

int isPointIn(point p) {
    int wn = 0;
    for(int i = 0; i < n; i++) {
        if(OnSegment(p, v[i], v[(i+1)%n])) return 1;
        int k = dcmp(Cross(v[(i+1)%n]-v[i], p-v[i]));
        int d1 = dcmp(v[i].y-p.y);
        int d2 = dcmp(v[(i+1)%n].y-p.y);
        if(k>0 && d1<=0 && d2 > 0) wn++;
        if(k<0 && d2<=0 && d1 > 0) wn--;
    }
    if(wn!=0) return 1;
    else return 0;
}


int main()
{
    int T = 1;
    point tmp;
    bool first = false;
    while(scanf("%d", &n)!=EOF && n) {
        if(first) printf("\n");
        else first = true;
        scanf("%d", &m);
        v.clear();
        Contain.clear();
        for(int i = 0; i < n; i++) {
            scanf("%d%d", &tmp.x, &tmp.y);
            Contain.push_back(tmp);
        }
        for(int i = n-1; i >= 0; i--) {
            v.push_back(Contain[i]);
        }
        check.clear();
        for(int i = 0; i < m; i++) {
            scanf("%d%d", &tmp.x, &tmp.y);
            check.push_back(tmp);
        }
        printf("Problem %d:\n", T++);
        for(int i = 0; i < m; i++) {
            int res = isPointIn(check[i]);
            if(res==1) printf("Within\n");
            else printf("Outside\n");
        }
    }
}