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C++容器与算法

news 来源：原创 2024/5/2 7:32:30

容器：某一类型数据的集合。

C++标准顺序容器包括：vector，list，queue

容器初始化

        vector<int> t;
        for (int i = 0; i < 50; i ++) {
                t.push_back(i);
        }

        vector<int> c; // 空容器
        vector<int> c1(t); // 容器t的副本
        vector<int> c2(3, 4); // 3个值为4的容器
        vector<int> c3(t.begin(), t.end() - 10); // 容器t的begin()和end()-10之前的数据副本
        vector<int> c4(5); // 创建包含5个空默认值的副本

容器类型的规则：支持复制和赋值操作

容器的迭代访问

窗口的迭代访问非常类似指针的操作，都支持++和--的位移操作，迭代器内置了操作符重载。

*item
item->num
++item
item++
--item
item--
iter1 == iter2
iter1 != iter2

迭代器访问

for (vector<string>::iterator iter = strs2.begin(); iter != strs2.end(); iter ++) {
        std::cout << *iter << std::endl;
    }

迭代器的首元素迭代器和尾元素迭代器可以通过begin()和end()方法获取，并通过++方法进行迭代。

迭代器操作的API：

Iterators:

begin Return iterator to beginning (public member function )

end Return iterator to end (public member function )

rbegin Return reverse iterator to reverse beginning (public member function)

rend Return reverse iterator to reverse end (public member function) 容器的元素类型

Member types

of template <class T, class Allocator=allocator<T> > class vector;

member type	definition
`reference`	`Allocator::reference`
`const_reference`	`Allocator::const_reference`
`iterator`	Random access iterator
`const_iterator`	Constant random access iterator
`size_type`	Unsigned integral type (usually same as size_t)
`difference_type`	Signed integral type (usually same as ptrdiff_t)
`value_type`	`T`
`allocator_type`	`Allocator`
`pointer`	`Allocator::pointer`
`const_pointer`	`Allocator::const_pointer`
`reverse_iterator`	`reverse_iterator<iterator>`
`const_reverse_iterator`	`reverse_iterator<const_iterator>`

通过reverse类型属性，可以逆序访问容器的迭代器

增加和删除元素

容器的API提供在具体什么位置增加或者删除元素，或者在什么元素增加或者删除元素：

Modifiers:

assign Assign vector content (public member function)

push_back Add element at the end (public member function)

pop_back Delete last element (public member function)

insert Insert elements (public member function)

erase Erase elements (public member function )

swap Swap content (public member function )

clear Clear content (public member function)

容器大小

Capacity:

size Return size (public member function)

max_size Return maximum size (public member function )

resize Change size (public member function)

capacity Return size of allocated storage capacity (public member function)

empty Test whether vector is empty (public member function)

reserve Request a change in capacity (public member function)

关联容器

C++中的关联容器包括 map 和 set

map与key, value相对应，整合起来map与pair类型对应

set 直接与 value相对应

同时存在multimap和multiset两个对象，支持一个key对应多个value

具体可以参考：

http://www.cplusplus.com/reference/stl/map/

C++的容器算法

最常见的是find方法，C++中的示例：

// 包含必要的头文件

#include <algorithm>

vector<int> vec(2, 35);
vec.push_back(8);
vec.push_back(80);
vec.push_back(98);
vec.push_back(25);
vec.push_back(12);
vector<int>::const_iterator result = find(vec.begin(), vec.end(), 80);
std::cout << 80 << (result == vec.end() ? " is not present" : " is present") << std::endl;

除了少数情况下，C++的容器算法都是在一个范围内的元素进行操作。所以其参数顺序情况一般为：iter_begin, iter_end, search_value。

C++容器使用的算法与数据结构书中大致相同：

1. 只读算法（查找）

2. 写算法（排序）

3. 合并

4. 堆

5. 最大/最小值等

常用只读算法：

....

实践了fill, fill_n, back_inserter, copy, replace, sort, count_if

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
using namespace std;
void log(std::string log) {
    std::cout << log << std::endl;
}
void apiTest() {
}
int main()
{
    vector<int> vec(2, 10);
    vec.push_back(3);
    vec.push_back(4);
    vec.push_back(15);
    vec.push_back(45);
    vec.push_back(24);
    vec.push_back(234);
    fill(vec.begin() + 1, vec.end() - 2,3);
    fill_n(back_inserter(vec), 10, 2);
    replace(vec.end() - 5, vec.end(), 2, 8);
    vector<int>::const_iterator iter = vec.begin();
    for (;iter != vec.end();iter++) {
        std::cout << *iter << std::endl;
    }
    vector<int> vec2;
    copy(vec.begin(), vec.end(), back_inserter(vec2));
    return 0;
}