UVa 10256 The Great Divide，推断两个凸包是否相离

先从给出的两个点集中分别计算出两个凸包，

然后推断两个凸包是否相离。

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

const double eps = 1e-10;
double dcmp(double x) {
    if(fabs(x) < eps) return 0;
    else return x < 0 ?
 -1 : 1;
}

struct Point {
    double x, y;
    Point(double x=0, double y=0):x(x),y(y) {}
};

typedef Point Vector;

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

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

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

bool operator < (const Point& p1, const Point& p2) {
    return p1.x < p2.x || (p1.x == p2.x && p1.y < p2.y);
}

bool operator == (const Point& p1, const Point& p2) {
    return p1.x == p2.x && p1.y == p2.y;
}

bool SegmentProperIntersection(const Point& a1, const Point& a2, const Point& b1, const Point& b2) {
    double c1 = Cross(a2-a1,b1-a1), c2 = Cross(a2-a1,b2-a1),
           c3 = Cross(b2-b1,a1-b1), c4=Cross(b2-b1,a2-b1);
    return dcmp(c1)*dcmp(c2)<0 && dcmp(c3)*dcmp(c4)<0;
}

bool OnSegment(const Point& p, const Point& a1, const Point& a2) {
    return dcmp(Cross(a1-p, a2-p)) == 0 && dcmp(Dot(a1-p, a2-p)) < 0;
}

// 点集凸包
// 假设不希望在凸包的边上有输入点，把两个 <= 改成 <
// 假设不介意点集被改动，能够改成传递引用
vector<Point> ConvexHull(vector<Point> p) {
    // 预处理，删除反复点
    sort(p.begin(), p.end());
    p.erase(unique(p.begin(), p.end()), p.end());

    int n = p.size();
    int m = 0;
    vector<Point> ch(n+1);
    for(int i = 0; i < n; i++) {
        while(m > 1 && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2]) <= 0) m--;
        ch[m++] = p[i];
    }
    int k = m;
    for(int i = n-2; i >= 0; i--) {
        while(m > k && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2]) <= 0) m--;
        ch[m++] = p[i];
    }
    if(n > 1) m--;
    ch.resize(m);
    return ch;
}

int IsPointInPolygon(const Point& p, const vector<Point>& poly) {
    int wn = 0;
    int n = poly.size();
    for(int i=0; i<n; ++i) {
        const Point& p1 = poly[i];
        const Point& p2 = poly[(i+1)%n];
        if(p1 == p || p2 == p || OnSegment(p, p1, p2)) return -1;//在边界上
        int k = dcmp(Cross(p2-p1, p-p1));
        int d1 = dcmp(p1.y - p.y);
        int d2 = dcmp(p2.y - p.y);
        if(k > 0 && d1 <= 0 && d2 > 0) wn++;
        if(k < 0 && d2 <= 0 && d1 > 0) wn--;
    }
    if(wn != 0) return 1;
    return 0;
}


bool ConvexPolygonDisjoint(const vector<Point> ch1, const vector<Point> ch2) {
    int c1 = ch1.size();
    int c2 = ch2.size();
    for(int i=0; i<c1; ++i)
        if(IsPointInPolygon(ch1[i], ch2) != 0) return false;
    for(int i=0; i<c2; ++i)
        if(IsPointInPolygon(ch2[i], ch1) != 0) return false;
    for(int i=0; i<c1; ++i)
        for(int j=0; j<c2; ++j)
            if(SegmentProperIntersection(ch1[i], ch1[(i+1)%c1], ch2[j], ch2[(j+1)%c2])) return false;
    return true;
}

int main() {
    int n, m;
    while(scanf("%d%d", &n, &m) == 2 && n > 0 && m > 0) {
        vector<Point> P1, P2;
        double x, y;
        for(int i = 0; i < n; i++) {
            scanf("%lf%lf", &x, &y);
            P1.push_back(Point(x, y));
        }
        for(int i = 0; i < m; i++) {
            scanf("%lf%lf", &x, &y);
            P2.push_back(Point(x, y));
        }
        if(ConvexPolygonDisjoint(ConvexHull(P1), ConvexHull(P2)))
            printf("Yes
");
        else
            printf("No
");
    }
    return 0;
}