POJ 1127 Jack Straws (线段相交)

题意：给定一堆线段，然后有询问，问这两个线段是不是相交，并且如果间接相交也可以。

析：可以用并查集和线段相交来做，也可以用Floyd来做，相交就是一个模板题。

代码如下：

#pragma comment(linker, "/STACK:1024000000,1024000000")

#include <cstdio>

#include <string>

#include <cstdlib>

#include <cmath>

#include <iostream>

#include <cstring>

#include <set>

#include <queue>

#include <algorithm>

#include <vector>

#include <map>

#include <cctype>

#include <cmath>

#include <stack>

#include <sstream>

#define debug() puts("++++");

#define gcd(a, b) __gcd(a, b)

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define freopenr freopen("in.txt", "r", stdin)

#define freopenw freopen("out.txt", "w", stdout)

using namespace std;

typedef long long LL;

typedef unsigned long long ULL;

typedef pair<int, int> P;

const int INF = 0x3f3f3f3f;

const double inf = 0x3f3f3f3f3f3f;

const double PI = acos(-1.0);

const double eps = 1e-8;

const int maxn = 100 + 10;

const int mod = 1e9 + 7;

const int dr[] = {-1, 0, 1, 0};

const int dc[] = {0, 1, 0, -1};

const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};

int n, m;

const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

inline bool is_in(int r, int c){

  return r >= 0 && r < n && c >= 0 && c < m;

}

struct Point{

  double x, y;

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

};

typedef Point Vector;

int dcmp(double x){

  if(fabs(x) < eps) return 0;

  return x < 0 ? -1 : 1;

}

Vector operator + (Vector A, Vector B){ return Vector(A.x+B.x, A.y+B.y); }

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

Vector operator + (Vector A, double p){ return Vector(A.x*p, A.y*p); }

bool operator == (const Point &a, const Point &b){ return dcmp(a.x-b.x) == 0 && dcmp(a.y-b.y) == 0; }

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

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

struct Node{

  Point p, q;

};

Node a[maxn];

int p[maxn];

int Find(int x){ return x == p[x] ? x : p[x] = Find(p[x]); }

bool onSegment(Point p, Point a1, Point a2){

  return dcmp(Cross(a1-p, a2-p)) == 0 && dcmp(Dot(a1-p, a2-p)) < 0;

}

bool judge(int i, int j){

  if(onSegment(a[i].p, a[j].p, a[j].q))  return true;

  if(onSegment(a[i].q, a[j].p, a[j].q))  return true;

  if(onSegment(a[j].p, a[i].p, a[i].q))  return true;

  if(onSegment(a[j].q, a[i].p, a[i].q))  return true;

  if(a[i].p == a[j].q || a[i].p == a[j].p || a[i].q == a[j].p || a[i].q == a[j].q)  return true;

  double c1 = Cross(a[i].q-a[i].p, a[j].p-a[i].p);

  double c2 = Cross(a[i].q-a[i].p, a[j].q-a[i].p);

  double c3 = Cross(a[j].q-a[j].p, a[i].p-a[j].p);

  double c4 = Cross(a[j].q-a[j].p, a[i].q-a[j].p);

  return dcmp(c1) * dcmp(c2) < 0 && dcmp(c3) * dcmp(c4) < 0;

}

int main(){

  while(scanf("%d", &n) == 1 && n){

    for(int i = 1; i <= n; ++i){

      p[i] = i;

      scanf("%lf %lf %lf %lf", &a[i].p.x, &a[i].p.y, &a[i].q.x, &a[i].q.y);

    }

    for(int i = 1; i <= n; ++i){

      int x = Find(i);

      for(int j = 1 + i; j <= n; ++j){

        int y = Find(j);

        if(x == y)  continue;

        if(judge(i, j))  p[y] = x;

      }

    }

    int x, y;

    while(scanf("%d %d", &x, &y) == 2 && x+y){

      x = Find(x);

      y = Find(y);

      if(x == y)  puts("CONNECTED");

      else  puts("NOT CONNECTED");

    }

  }

  return 0;

}