poj 2653 Pick-up sticks（判断线段是否相交）

最新推荐文章于 2022-06-20 22:52:35 发布

wlyqh

最新推荐文章于 2022-06-20 22:52:35 发布

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分类专栏：计算几何文章标签： struct c

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【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 <string>
#include <algorithm>
#include <cmath>

using namespace std;

#define eps 1e-8

struct 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;
}

【运行结果】：