HDU

枚举判断线段相交

6个条件判相交（叉积）

跟上篇博客差不多

#include<iostream>#include<algorithm>#include<cstdio>#include<cstdlib>#include<cstring>#include<string>#include<cmath>#include<set>#include<queue>#include<stack>#include<map>#define PI acos(-1.0)#define in freopen("in.txt", "r", stdin)#define out freopen("out.txt", "w", stdout)using namespace std;typedef long long ll;typedef unsigned long long ull;const int maxn = 100 + 7, maxd = 100 + 7, mod = 1e9 + 7;const ll INF = 0x7f7f7f7f;int n;struct node {    double x, y;}a[maxn], b[maxn];double area(node a, node b, node c) {    return (b.x-a.x)*(c.y-a.y) - (b.y-a.y)*(c.x-a.x);}bool is_inter(node a, node b, node c, node d) {    if(       max(a.x, b.x) >= min(c.x, d.x) &&       max(c.x, d.x) >= min(a.x, b.x) &&       max(a.y, b.y) >= min(c.y, d.y) &&       max(c.y, d.y) >= min(a.y, d.y) &&       area(a, b, c) * area(a, b, d) <= 0 &&       area(c, d, a) * area(c, d, b) <= 0       ) return 1;    return 0;}int solve() {    int ans = 0;    for(int i = 1; i < n; ++i) {        for(int j = i+1; j <= n; ++j) {            if(is_inter(a[i], b[i], a[j], b[j])) ans++;            //cout << ans << endl;        }    }    return ans;}int main() {    while(~scanf("%d", &n) && n) {        for(int i = 1; i <= n; ++i) {            scanf("%lf%lf%lf%lf", &a[i].x, &a[i].y, &b[i].x, &b[i].y);        }        //cout << " ==== " << endl;        printf("%d\n", solve());    }    return 0;}