#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;

};

}