URAL 1966

几何模板

#include<cstdio>#include<cstring>#include<algorithm>#include<iostream>#include<cmath>using namespace std;const double eps = 1e-8;int dcmp(double d) {    return d < -eps ? -1 : d > eps;}struct Point {    double x, y;    Point() {}    Point(double x, double y)    : x(x), y(y) {}    Point operator + (const Point& a) const {        return Point(x + a.x, y + a.y);    }    Point operator - (const Point& a) const {        return Point(x - a.x, y - a.y);    }    Point operator * (double k) const {        return Point(x * k, y * k);    }    Point operator / (double k) const {        return Point(x / k, y / k);    }    double cross(const Point& a) const {        return (x * a.y - y * a.x);    }    double dot(const Point& a) const {        return x * a.x + y * a.y;    }    void read() {        scanf("%lf%lf", &x, &y);    }    bool operator < (const Point& a) const {        return x < a.x || (x == a.x && y < a.y);    }    bool operator == (const Point& a) const {        return dcmp(x - a.x) == 0 && dcmp(y - a.y) == 0;    }    double length() {        return sqrt(x * x + y * y);    }};struct Line {    Point a, b;    Line() {}    Line(const Point& a, const Point& b)    :a(a), b(b) {}    bool onSegment(Point p) {// 判断点是否在线段上         return dcmp((p - a).cross(b - a)) == 0 && dcmp((a - p).dot(b - p)) <= 0;    }    int segCrossSeg(const Line &u) {// 判断线段是否相交         int d1 = dcmp((b - u.a).cross(a - u.a));        int d2 = dcmp((b - u.b).cross(a - u.b));        int d3 = dcmp((u.b - a).cross(u.a - a));        int d4 = dcmp((u.b - b).cross(u.a - b));        if ((d1 ^ d2) == -2 && (d3 ^ d4) == -2) return 2;        return ((d1 == 0 && dcmp((b - u.a).dot(a - u.a)) <= 0)            || (d2 == 0 && dcmp((b - u.b).dot(a - u.b)) <= 0)            || (d3 == 0 && dcmp((u.b - a).dot(u.a - a)) <= 0)            || (d4 == 0 && dcmp((u.b - b).dot(u.a - b)) <= 0));    }};//************************模板********************************************// Point p[250];int fa[250];int eu[250],ev[250];int n,m;int getFather(int x){if(fa[x]==-1)return x;return fa[x]=getFather(fa[x]);}int main() {while(cin>>n>>m){memset(fa,-1,sizeof(fa));for(int i=1;i<=n;i++)p[i].read();for(int i=1;i<=m;i++){cin>>eu[i]>>ev[i];int fu=getFather(eu[i]);int fv=getFather(ev[i]);if(fu!=fv)fa[fu]=fv;}for(int i=1;i<=m;i++){Line l(p[eu[i]],p[ev[i]]);for(int j=1;j<=n;j++){if(l.onSegment(p[j])==0)continue;int fu=getFather(j);int fv=getFather(eu[i]);if(fu!=fv)fa[fu]=fv;}}for(int i=1;i<=m;i++)for(int j=i+1;j<=m;j++){Line l1(p[eu[i]],p[ev[i]]);Line l2(p[eu[j]],p[ev[j]]);if(l1.segCrossSeg(l2)==0)continue;int fu=getFather(eu[j]);int fv=getFather(eu[i]);if(fu!=fv)fa[fu]=fv;}int cnt=0;for(int i=1;i<=n;i++)if(fa[i]==-1)cnt++; if (cnt == 1) puts("YES");    else puts("NO");}    return 0;}