FZUACM Problem 1120 A Pilot in Danger!
#include <iostream>
#include <cmath>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;
//2013-06-05 17:19:28 Accepted 1120 GNU C++ 0 ms 856KB 2352B
const double eps = 1e-8;
int dcmp(double x) {
if(fabs(x) < eps) return 0;
if(x > 0) return 1;
return -1;
}
struct point {
double x, y;
point() {}
point(double a, double b) : x(a), y(b) {}
friend point operator - (const point &a, const point &b) {
return point(a.x-b.x, a.y-b.y);
}
friend point operator + (const point &a, const point &b) {
return point(a.x+b.x, a.y+b.y);
}
};
double det(const point &a, const point &b) {
return a.x * b.y - a.y * b.x;
}
double dot(const point &a, const point &b) {
return a.x*b.x + a.y*b.y;
}
bool PointOnSegment(point p, point s, point t) {
return dcmp(det(p-s, t-s))==0 && (dcmp(dot(p-s, p-t))<=0);
}
const int maxn = 40100;
//多边形的点顺时针，逆时针都可以。
struct polygon {
int n;
point a[maxn];
//polygon() {}
int Point_In(point t) {
int num = 0, i, d1, d2, k;
a[n] = a[0];
for(i = 0; i < n; i++) {
if(PointOnSegment(t, a[i], a[i+1])) return 2;
k = dcmp(det(a[i+1]-a[i], t-a[i]));
d1 = dcmp(a[i].y - t.y);
d2 = dcmp(a[i+1].y - t.y);
if(k>0 && d1<=0 && d2>0) num++;
if(k<0 && d2<= 0 && d1>0) num--;
}
if(num!=0) return 1;//在多边形内。
return 0;
}
};
polygon v;
int main()
{
int n;
int p, q;
int num = 0;
while(scanf("%d", &n) != EOF) {
if(n==0) break;
v.n = n;
for(int i = 0; i < n; i++) {
scanf("%lf%lf", &v.a[i].x, &v.a[i].y);
}
scanf("%d%d", &p, &q);
int secret = (p-1)*(q-1)/2;
int res = v.Point_In(point(0, 0));
printf("Pilot %d\n", ++num);
if(res==1) {
printf("The pilot is in danger!\n");
printf("The secret number is %d.\n", secret);
} else {
printf("The pilot is safe.\n");
}
cout << endl;
}
}