【BZOJ1007】[HNOI2008]水平可见直线【半平面交】

来源：互联网发布：云南进出口贸易数据编辑：程序博客网时间：2024/06/05 03:08

【题目链接】

学习一发计算几何基础。

/* Telekinetic Forest Guard */#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>using namespace std;typedef double DB;const int maxn = 50005;const DB eps = 1e-6;struct _line {DB k, b;int id;} l[maxn];int n, sta[maxn], top;inline bool cmp(_line x, _line y) {return fabs(x.k - y.k) < eps ? x.b < y.b : x.k < y.k;}inline bool cmp2(int x, int y) {return l[x].id < l[y].id;}inline DB cosp(_line x, _line y) {return (x.b - y.b) / (y.k - x.k);}inline void insert(int id) {while(top) {if(fabs(l[sta[top]].k - l[id].k) < eps) top--;else if(top > 1 && cosp(l[id], l[sta[top - 1]]) <= cosp(l[sta[top]], l[sta[top - 1]])) top--;else break;}sta[++top] = id;}int main() {scanf("%d", &n);for(int i = 1; i <= n; i++) scanf("%lf%lf", &l[i].k, &l[i].b), l[i].id = i;sort(l + 1, l + 1 + n, cmp);top = 0;for(int i = 1; i <= n; i++) insert(i);sort(sta + 1, sta + 1 + top, cmp2);for(int i = 1; i <= top; i++) printf("%d ", l[sta[i]].id);return 0;}

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