20190211update:工作的时候看同事ocr的代码，发现有一段就是极角排序orz...所以说算法还是有用的...

先介绍几种极角排序：

1.利用叉积的正负来作cmp.(即是按逆时针排序).此题就是用这种方法

A - You can Solve a Geometry Problem too

**Time Limit:**1000MS **Memory Limit:**32768KB 64bit IO Format:%I64d & %I64u

Submit Status

Description

Many geometry（几何）problems were designed in the ACM/ICPC. And now, I also prepare a geometry problem for this final exam. According to the experience of many ACMers, …

改革春风吹满地

**Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 24179 Accepted Submission(s): 12504
**

Problem Description

" 改革春风吹满地,
不会AC没关系;
实在不行回老家，
还有一亩三分地。
谢谢!（乐队奏乐）"

B. Anton and Lines

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

The teacher gave Anton a large geometry homework, but he didn't do it (as usual) as he participated in a regular round on Codeforces. In the task he was given a set of n lines defined by the …

A. 2Char

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Andrew often reads articles in his favorite magazine 2Char. The main feature of these articles is that each of them uses at most two distinct letters. Andrew decided to send an article to the magazine, …