poj 2653 Pick-up sticks

来源：互联网发布：淘宝客服售后面试问题编辑：程序博客网时间：2024/05/19 22:45

题意：
按顺序给出线段, 上面的可能会覆盖下面的, 求出不被其他线段覆盖的所有线段

分析：暴力搜索,如果一条线段不被后面任一条覆盖,则它是答案之一

重点：线段的平行,相交,点与线段的位置关系的判定, 点积叉积的灵活运用。

#include <cstdio>#include <cstring>#include <string>#include <cmath>#include <algorithm>#include <vector>#include <queue>#define MAX 100005#include <iostream>#define PI acos(-1.0)#define eps 1e-5#define INF 1e8using namespace std;inline int sgn(double x){ return x < -eps ? -1 : ( x > eps ? 1 : 0) ;}struct Point{    double x, y;    Point(){}    Point(double xx, double yy):x(xx), y(yy){}    Point operator - (const Point &p)const{        return Point(x - p.x, y - p.y);    }    void input(){        cin>>x>>y;    }    void output(){        cout<<x<<y<<endl;    }    friend double det(const Point &p1, const Point &p2){        return p1.x * p2.y - p1.y * p2.x;    }    friend double dot(const Point &p1, const Point &p2){        return p1.x *p2.x + p1.y * p2.y;    }    friend Point operator * (const Point &p1, const double &w){        return Point(p1.x * w, p1.y * w);    }    friend Point operator / (const Point &p1, const double &w){        return Point(p1.x/ w, p1.y/ w);    }};struct Line{    Point s, t;    Line(){}    Line(const Point &p1, const Point &p2):s(p1), t(p2){}    void input(){        s.input();        t.input();    }    bool isParell(const Line &line) const{        if(sgn( det(line.t - line.s, t - s) ) == 0 ){            return true;        }        return false;    }    bool InsectPoint(Point &res, const Line &line)const{            if(isParell(line))return false;            double s1  =  det( t - s, line.s - s);            double s2  =  det( t - s, line.t - s);            res = (line.t * s1 - line.s * s2) / (s1 - s2);            return true;    }    bool isOnLine(const Point &p1)const{//包括两端        return ( sgn( det(p1 - s, t - s) ) == 0 && sgn(dot(p1 - s, p1 - t) ) <= 0);    }    bool isInsect(const Line &line)const{        Point res;        if(!InsectPoint(res, line)){//            puts("parell");            return false;        }//        puts("not parell");//        res.output();        return (isOnLine(res) && line.isOnLine(res));    }}line[MAX];int main(){    int n;    while(cin>>n, n){        for(int i = 0; i < n;i++){            line[i].input();        }//        cout<<line[0].isInsect(line[1])<<endl;        printf("Top sticks: ");        vector<int>ans;        for(int i = 0; i < n; i++){            bool isFind = true;            for(int j = i + 1; j < n; j++){                if(line[i].isInsect(line[j])){                    isFind = false;                    break;                }            }            if(isFind)ans.push_back(i + 1);        }        int tSize = ans.size();        for(int i = 0; i < tSize - 1; i++){            printf("%d, ", ans[i]);        }printf("%d.\n", ans[tSize - 1]);    }    return 0;}