资料
http://hivemined.ir/wp-content/uploads/2012/04/convexHull.pdf
http://en.literateprograms.org/Quickhull_%28Python%2C_arrays%29
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <map>
#include <ctime>
using namespace std;
#define MIN(a, b) ((a) < (b) ? (a) : (b))