poj 2653 Pick-up sticks（判断线段是否相交）

//以下为原blog搬迁过来的内容

【题目大意】：给出n条木棍，然后依次摆放在桌面上，每次摆放的木棍的起始点和终止点给定，求最上面的木棍的标号

 

【解题思路】：线段判相交就是了，水题

 

【代码】：

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <vector>#include <queue>#include <cmath>#include <string>#include <cctype>#include <map>#include <iomanip>                   using namespace std;                   #define eps 1e-8#define pi acos(-1.0)#define inf 1<<30#define pb push_back#define lc(x) (x << 1)#define rc(x) (x << 1 | 1)#define lowbit(x) (x & (-x))#define ll long longstruct Point{    double x, y;    Point() {}    Point(double a, double b)    {        x = a, y = b;    }}point[200000];struct Line{    Point a, b;    Line() {}    Line(Point x, Point y)    {        a = x, b = y;    }}line[150000];int judge[150000],n,m;double p,q;inline int sig(double k){    return k < -eps ? -1 : k > eps;}inline double det(double x1, double y1, double x2, double y2){    return x1 * y2 - x2 * y1;}inline double xmult(Point o, Point a, Point b){    return det(a.x - o.x, a.y - o.y, b.x - o.x, b.y - o.y);}inline double dotdet(double x1, double y1, double x2, double y2){    return x1 * x2 + y1 * y2;}inline double dot(Point o, Point a, Point b){    return dotdet(a.x - o.x, a.y - o.y, b.x - o.x, b.y - o.y);}inline int between(Point o, Point a, Point b){    return sig(dot(o, a, b));}inline int intersect1(Point a, Point b, Point c, Point d){    double s1, s2, s3, s4;    int d1 = sig(s1 = xmult(a, b, c));    int d2 = sig(s2 = xmult(a, b, d));    int d3 = sig(s3 = xmult(c, d, a));    int d4 = sig(s4 = xmult(c, d, b));    if ((d1^d2) == -2 && (d3^d4) == -2)    {        return 1;    }    if (d1 == 0 && between(c, a, b) <= 0) return 2;    if (d2 == 0 && between(d, a, b) <= 0) return 2;    if (d3 == 0 && between(a, c, d) <= 0) return 2;    if (d4 == 0 && between(b, c, d) <= 0) return 2;    return 0;}inline int intersect(Line u, Line v){    return intersect1(u.a, u.b, v.a, v.b);}int main(){    while (~scanf("%d",&n))    {        if (n==0) break;        for (int i=0; i<n; i++)        {            scanf("%lf%lf",&p,&q);            point[2*i-1]=Point(p,q);            scanf("%lf%lf",&p,&q);            point[2*i]=Point(p,q);            line[i]=Line(point[2*i-1],point[2*i]);        }        memset(judge,0,sizeof(judge));        for (int i=0; i<n; i++)        {            for (int j=i+1; j<n; j++)            {                int k;                k=intersect(line[i],line[j]);                if (k!=0) {judge[i]=1; break;}            }        }        printf("Top sticks:");        for (int i=0; i<n-1; i++)        {            if (judge[i]==0)            printf(" %d,",i+1);        }        printf(" %d.\n",n);    }    return 0;}