CodeForces 801D 计算几何,水

#include<bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:102400000,102400000")
#define rep(i,a,b) for (int i=a;i<=b;i++)
#define per(i,b,a) for (int i=b;i>=a;i--)
#define mes(a,b)  memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
#define MP make_pair
#define PB push_back
#define fi  first
#define se  second
#define eps  1e-6
typedef long long ll;
const int N = 2005;

int n;
struct Point { double x, y; } p[N];
double dis(Point a, Point b)
{
    return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
}
double Heron(double a, double b, double c)
{
    double p=(a+b+c)/2;
    return sqrt(p*(p-a)*(p-b)*(p-c));
}
double getsqr(Point a, Point b, Point c)
{
    return Heron(dis(a,b), dis(b,c), dis(a,c));
}
int main()
{
    scanf("%d", &n);
    rep(i,1,n) scanf("%lf %lf", &p[i].x, &p[i].y);
    p[n+1]=p[1], p[n+2]=p[2];
    double ans=4.6e18;
    rep(i,3,n+2)
    {
        double len=getsqr(p[i-2], p[i-1], p[i])/dis(p[i-2],p[i]);
        ans=min(ans, len);
    }
    printf("%.6f\n", ans);

    return 0;
}