NYOJ 1016 判断两线段是否相交

#include<cstdio>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<vector>
#include<stack>
#include<cstring>
#include<queue>
#include<set>
#include<string>
#include<map>
#include <time.h>
#define PI acos(-1)
using namespace std;
typedef long long ll;
typedef double db;
const int maxn = 400005+1000;
const int sigma=26;
const ll mod = 1000000007;
const int INF = 0x3f3f3f;
const db eps = 1e-9;
struct point {
    db x, y;
    point(db x=0, db y=0):x(x), y(y) {}
}s1, e1, s2, e2;

typedef point Vector;
Vector operator - (point A, point B) {
    return Vector(A.x-B.x, A.y-B.y);
}
db Cross(point A, point B) {
   return A.x*B.y-B.x*A.y;
}
void solve() {
    scanf("%lf%lf%lf%lf", &s1.x, &s1.y, &e1.x, &e1.y);
    scanf("%lf%lf%lf%lf", &s2.x, &s2.y, &e2.x, &e2.y);
    Vector CA=s1-s2;
    Vector CD=e2-s2;
    Vector CB=e1-s2;
    db s=Cross(CA, CD)*Cross(CB, CD);
    Vector AC=s2-s1;
    Vector AB=e1-s1;
    Vector AD=e2-s1;  
    db ss=Cross(AC, AB)*Cross(AD, AB);
   // cout<<s<<" "<<ss<<endl;
    if (s<=0 && ss<=0)  puts("Interseetion");
    else  puts("Not Interseetion");
}
int main() {
    int t = 1;
   // freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    scanf("%d", &t);
    while(t--) {
        solve();
    }
    return 0;
}