BZOJ 1007: [HNOI2008]水平可见直线

/*
BZOJ 1007: [HNOI2008]水平可见直线

SB半平面交
*/
#include <cstdio>
#include <iostream>
#include <algorithm>
typedef double flo;
#define Max 50004
#define rg register
struct L
{
flo k, b; int id;
bool operator < (const L &A) const
{
return k == A.k ? b > A.b : k < A.k;
}
flo operator & (const L &A) const
{
return (A.b - b) / (k - A.k);
}
} l[Max]; int s[Max], t;
bool Comp (const int &a, const int &b)
{
return l[a].id < l[b].id;
}
int main (int argc, char *argv[])
{
int N, M; rg int i, j; scanf ("%d", &N);
for (i = 1; i <= N; ++ i) scanf ("%lf%lf", &l[i].k, &l[i].b), l[i].id = i;
std :: sort (l + 1, l + 1 + N); s[++ t] = 1;
for (i = 2; i <= N; ++ i)
{
if (l[i].k == l[i - 1].k) continue;
for (; t > 1 && (l[i] & l[s[t - 1]]) <= (l[s[t - 1]] & l[s[t]]); -- t);
s[++ t] = i;
}
std :: sort (s + 1, s + 1 + t, Comp); for (i = 1; i <= t; ++ i) printf ("%d ", l[s[i]].id);
return 0;
}