#include<iostream>
#include<string.h>
#include<assert.h>
using namespace std;

namespace myvector
{
	template<class T>
	class vector
	{
	public:
		typedef T* iterator;

		iterator begin()
		{
			return start;
		}

		iterator end()
		{
			return finish;
		}

		//默认构造函数
		vector()
			:start(nullptr)
			, finish(nullptr)
			, end_of_storage(nullptr)
		{}
		//容量
		size_t capacity()
		{
			return end_of_storage - start;
		}

		size_t size()
		{
			return finish - start;
		}

		void reserve(size_t n)
		{
			if (n > capacity())
			{
				//开新空间
				T* tmp = new T[n];
				//拷贝旧空间的内容
				memcpy(tmp, start, sizeof(T)*size());
				//改变容量
				finish = tmp + size();
				end_of_storage = tmp + n;
				//释放旧空间
				T* tmp1 = start;
				start = tmp;
				tmp = nullptr;
			}
		}

		void resize(size_t n, const T& val = T())
		{
			//判断容量
			if (n > capacity())
				reserve(n);
			//如果n<size
			if (n < size())
			{
				finish = start + n;
			}
			else
			{
				while (finish != start + n)
				{
					*finish = val;
					finish++;
				}
			}
		}
		//检查空间
		void check_capacity()
		{
			if (finish == end_of_storage)
			{
				//如果当前不为空，就扩2倍，为空就开4个吧
				size_t newcapacity = finish == nullptr ? 4 : capacity()*2;
				reserve(newcapacity);
			}
		}

		T& operator[](size_t pos)
		{
			assert(pos < size());
			return start[pos];
		}
		
		//插入
		void push_back(const T& x)
		{
			insert(finish,x);
		}

		iterator insert(iterator pos, const T& x)
		{
			assert(pos >= start && pos <= finish);
			size_t pos1 = pos - start;
			check_capacity();
			//解决迭代器失效
			pos = start + pos1;
			//移动数据
			iterator end = finish;
			while (end >= pos)
			{
				*(end + 1) = *end;
				end--;
			}
			//插入数据
			*pos = x;
			finish++;
			return pos;
		}

		//删除数据
		void pop_back()
		{
			assert(finish > start);
			finish--;
		}
		iterator erase(iterator pos)
		{
			assert(pos >= start && pos < finish);

			iterator it = pos + 1;
			while (it != finish)
			{
				*(it - 1) = *it;
				++it;
			}
			--finish;

			return pos;
		}
		//析构函数
		~vector()
		{
			delete[] start;
			start = finish = end_of_storage = nullptr;
		}
	private:
		iterator start;
		iterator finish;
		iterator end_of_storage;
	};
}