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实现以下功能：

1. 构造函数：a.无参默认构造    b.n个val构造    c.迭代器区间构造    d.initializer_list构造，类似于数组    e.拷贝构造

2. =赋值重载

3. [ ]重载

4. 实现reserve接口

5. 实现size()，capacity()接口

6. 实现push_bakc接口，尾插

7. 实现insert接口，位置插入

8. 实现erase接口，位置删除

9. 实现pop_back接口，尾删

10. 实现empty接口，判断容器是否为空

11. 实现迭代器

#pragma once
#include<assert.h>
#include<iostream>
#include<algorithm>
using namespace std;/*
inrsert
push_backpop_back
erasereserve
capacity()
size()
empty()begin()
end()operator[]
*/namespace liu
{template<class T>class vector{public:typedef T* iterator;typedef const T* const_iterator;vector():_start(nullptr),_finish(nullptr),_endofstorage(nullptr){}~vector(){if (_start){delete[] _start;}_start = nullptr;_finish = nullptr;_endofstorage = nullptr;}template<class InputIterator>vector(InputIterator first, InputIterator last)//迭代器区间初始化{while (first!=last){push_back(*first);++first;}}vector(size_t n, const T& val = T())//n个VAL初始化{reserve(n);//提前开好空间，减少消耗for (size_t i=0;i<n;i++){push_back(val);}}vector(int n, const T& val = T()){reserve(n);//提前开好空间，减少消耗for (int i = 0; i < n; i++){push_back(val);}}//v2(v1)vector(const vector<T>& v)//拷贝构造:_start(nullptr), _finish(nullptr), _endofstorage(nullptr){reserve(v.capacity());for (auto& e:v){push_back(e);}}vector(initializer_list<T> il){reserve(il.size());{for (auto& e:il){push_back(e);}}}void swap(vector<T>& v){std::swap(_start,v._start);std::swap(_finish,v._finish);std::swap(_endofstorage,v._endofstorage);}vector<T>& operator=(vector<T> v){swap(v);return *this;}iterator begin(){return _start;}iterator end(){return _finish;}const_iterator begin()const{return _start;}const_iterator end()const{return _finish;}T& operator[](size_t i){assert(i<size());return _start[i];}const T& operator[](size_t i)const{assert(i < size());return _start[i];}void reserve(size_t n)//不仅是内部用，还要提供给外部用{if (n>capacity()){size_t oldSize = size();T* tmp = new T[n];if (_start){for (size_t i=0;i<oldSize;i++){tmp[i] = _start[i];}delete[] _start;}_start = tmp;_finish = _start + oldSize;_endofstorage = _start + n;}}size_t size(){return _finish - _start;}size_t capacity(){return _endofstorage - _start;}void push_back(const T& x){if (_finish==_endofstorage){reserve(capacity()==0?4:2*capacity());}*_finish = x;_finish++;}iterator insert(iterator pos,const T& val){assert(pos>=_start&&pos<=_finish);if (_finish==_endofstorage){size_t len = pos - _start;reserve(capacity() == 0 ? 4 : 2 * capacity());pos = _start + len;}iterator i = _finish-1;while(i>=pos){*(i + 1) = *i;i--;}*pos = val;++_finish;return pos;//更新迭代器}iterator erase(iterator pos){assert(pos >= _start && pos < _finish);iterator i = pos+1;while (i<_finish){*(i-1) = *i;i++;}--_finish;return pos;}void pop_back(){assert(!empty());_finish--;}bool empty(){return _start == _endofstorage;}private:iterator _start;iterator _finish;iterator _endofstorage;};
}