Algorithm库常用函数总结

文章目录

• Algorithm库常用函数总结
• Functions in <algorithm>所有函数
• 常用的函数
• 1、max()、min()、abs()比较数字
• 2、*max_element()、*min_element()比较容器（数组、字符串等）
• 3、swap()交换值
• 4、reverse()翻转容器
• 5、快速排序——sort函数

Algorithm库常用函数总结

可以去cplusplus官方网站查询，地址http://www.cplusplus.com/reference/algorithm/

☁️algorithm是C++中Stl的标准模板库，<algorithm>专门设计用于元素范围范围是可以通过迭代器或指针(例如数组或某些STL容器的实例)访问的任何对象序列。但是请注意，算法通过迭代器直接对这些值进行操作，不以任何方式影响任何可能的容器的结构(它从不影响容器的大小或存储分配)。

Functions in <algorithm>所有函数

🔽不想看可以跳过这一段列表，这里介绍Algorithm的所有操作，每个函数都有一个链接，点击即可到官网查看🔽

向下传送门⬅️

Non-modifying sequence operations:

• all_of

  Test condition on all elements in range (function template )

• any_of

  Test if any element in range fulfills condition (function template )

• none_of

  Test if no elements fulfill condition (function template )

• for_each

  Apply function to range (function template )

• find

  Find value in range (function template )

• find_if

  Find element in range (function template )

• find_if_not

  Find element in range (negative condition) (function template )

• find_end

  Find last subsequence in range (function template )

• find_first_of

  Find element from set in range (function template )

• adjacent_find

  Find equal adjacent elements in range (function template )

• count

  Count appearances of value in range (function template )

• count_if

  Return number of elements in range satisfying condition (function template )

• mismatch

  Return first position where two ranges differ (function template )

• equal

  Test whether the elements in two ranges are equal (function template )

• is_permutation

  Test whether range is permutation of another (function template )

• search

  Search range for subsequence (function template )

• search_n

  Search range for elements (function template )

Modifying sequence operations:

• copy

  Copy range of elements (function template )

• copy_n

  Copy elements (function template )

• copy_if

  Copy certain elements of range (function template )

• copy_backward

  Copy range of elements backward (function template )

• move

  Move range of elements (function template )

• move_backward

  Move range of elements backward (function template )

• swap

  Exchange values of two objects (function template )

• swap_ranges

  Exchange values of two ranges (function template )

• iter_swap

  Exchange values of objects pointed to by two iterators (function template )

• transform

  Transform range (function template )

• replace

  Replace value in range (function template )

• replace_if

  Replace values in range (function template )

• replace_copy

  Copy range replacing value (function template )

• replace_copy_if

  Copy range replacing value (function template )

• fill

  Fill range with value (function template )

• fill_n

  Fill sequence with value (function template )

• generate

  Generate values for range with function (function template )

• generate_n

  Generate values for sequence with function (function template )

• remove

  Remove value from range (function template )

• remove_if

  Remove elements from range (function template )

• remove_copy

  Copy range removing value (function template )

• remove_copy_if

  Copy range removing values (function template )

• unique

  Remove consecutive duplicates in range (function template )

• unique_copy

  Copy range removing duplicates (function template )

• reverse

  Reverse range (function template )

• reverse_copy

  Copy range reversed (function template )

• rotate

  Rotate left the elements in range (function template )

• rotate_copy

  Copy range rotated left (function template )

• random_shuffle

  Randomly rearrange elements in range (function template )

• shuffle

  Randomly rearrange elements in range using generator (function template )

Partitions:

• is_partitioned

  Test whether range is partitioned (function template )

• partition

  Partition range in two (function template )

• stable_partition

  Partition range in two - stable ordering (function template )

• partition_copy

  Partition range into two (function template )

• partition_point

  Get partition point (function template )

Sorting:

• sort

  Sort elements in range (function template )

• stable_sort

  Sort elements preserving order of equivalents (function template )

• partial_sort

  Partially sort elements in range (function template )

• partial_sort_copy

  Copy and partially sort range (function template )

• is_sorted

  Check whether range is sorted (function template )

• is_sorted_until

  Find first unsorted element in range (function template )

• nth_element

  Sort element in range (function template )

Binary search (operating on partitioned/sorted ranges):

• lower_bound

  Return iterator to lower bound (function template )

• upper_bound

  Return iterator to upper bound (function template )

• equal_range

  Get subrange of equal elements (function template )

• binary_search

  Test if value exists in sorted sequence (function template )

Merge (operating on sorted ranges):

• merge

  Merge sorted ranges (function template )

• inplace_merge

  Merge consecutive sorted ranges (function template )

• includes

  Test whether sorted range includes another sorted range (function template )

• set_union

  Union of two sorted ranges (function template )

• set_intersection

  Intersection of two sorted ranges (function template )

• set_difference

  Difference of two sorted ranges (function template )

• set_symmetric_difference

  Symmetric difference of two sorted ranges (function template )

Heap:

• push_heap

  Push element into heap range (function template )

• pop_heap

  Pop element from heap range (function template )

• make_heap

  Make heap from range (function template )

• sort_heap

  Sort elements of heap (function template )

• is_heap

  Test if range is heap (function template )

• is_heap_until

  Find first element not in heap order (function template )

Min/max:

• min

  Return the smallest (function template )

• max

  Return the largest (function template )

• minmax

  Return smallest and largest elements (function template )

• min_element

  Return smallest element in range (function template )

• max_element

  Return largest element in range (function template )

• minmax_element

  Return smallest and largest elements in range (function template )

Other:

• lexicographical_compare

  Lexicographical less-than comparison (function template )

• next_permutation

  Transform range to next permutation (function template )

• prev_permutation

  Transform range to previous permutation (function template )

常用的函数

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1、max()、min()、abs()比较数字

这个在math头文件也可以，浮点型的绝对值要用math的fabs

#include <iostream>
using namespace std;
int main()
{
    int a, b;
    cin >> a >> b;
    cout << max(a, b) << endl;
    cout << min(a, b) << endl;
    cout << abs(a - b) << endl;
    return 0;
}

2、*max_element()、*min_element()比较容器（数组、字符串等）

上面的max、min函数只能比较数字，如果比较数组等容器怎么办，就用*…_element()方法

// min_element/max_element example
#include <iostream>     // std::cout
#include <algorithm>    // std::min_element, std::max_element

bool myfn(int i, int j) { return i<j; }

struct myclass {
  bool operator() (int i,int j) { return i<j; }
} myobj;

int main () {
  int myints[] = {3,7,2,5,6,4,9};

  // using default comparison:
  std::cout << "The smallest element is " << *std::min_element(myints,myints+7) << '\n';
  std::cout << "The largest element is "  << *std::max_element(myints,myints+7) << '\n';

  // using function myfn as comp:
  std::cout << "The smallest element is " << *std::min_element(myints,myints+7,myfn) << '\n';
  std::cout << "The largest element is "  << *std::max_element(myints,myints+7,myfn) << '\n';

  // using object myobj as comp:
  std::cout << "The smallest element is " << *std::min_element(myints,myints+7,myobj) << '\n';
  std::cout << "The largest element is "  << *std::max_element(myints,myints+7,myobj) << '\n';

  return 0;
}

运行结果

The smallest element is 2
The largest element is 9
The smallest element is 2
The largest element is 9
The smallest element is 2
The largest element is 9

注意，min_element和max_element要加星号*，因为iterator迭代器，就加上就行了
下面是比较动态数组伪代码

std::vector<int>v;
v.push_back(10);
v.push_back(20);
v.push_back(30);
std::cout << *max_element(v.begin(), v.end()) << std::endl;

3、swap()交换值

这个一般不用algorithm库也可以实现swap函数，但还是比较常用

#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
    int a, b;
	swap(a, b);
    cout << a << " " << b << endl;
    int nums[4] = {0, 1, 2, 3};
    swap(nums[0], nums[3]);
    for (int i = 0; i < 3; i++)
        cout << nums[i] << " ";
    cout << endl;
    return 0;
}

4、reverse()翻转容器

reverse()函数可以将一个容器直接翻转，例如数组、动态数组和字符串等

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
int main()
{
    vector<int>array;//动态数组
    for (int i = 0; i < 5; i++)
    {
        int t;
        cin >> t;
        array.push_back(t);
    }
    reverse(array.begin(), array.end());
    for (int i = 0; i < array.size(); i++)
        cout << array[i] << " ";
    cout << endl;
    cout << "--------" << endl;
    string str = "hello world";//字符串
    reverse(str.begin(), str.end());
    cout << str << endl;
    cout << "--------" << endl;
    int arr1[101]; //数组
    for (int i = 0; i < 5; i++)
    {
        cin >> arr1[i];
    }
    reverse(arr1, arr1 + 5);
    for (int i = 0; i < 5; i++)
    {
        cout << arr1[i] << " ";
    }
    cout << endl;
    return 0;
}

输出结果：

1 2 3 4 5
5 4 3 2 1
--------
dlrow olleh
--------
5 2 6 4 5
5 4 6 2 5

5、快速排序——sort函数

快速排序，时间超短！
实例：

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
    vector<int> sortv; //动态数组
    for (int i = 0; i < 5; i++)
    {
        int t;
        cin >> t;
        sortv.push_back(t);
    }
    sort(sortv.begin(), sortv.end());
    for (int i = 0; i < 5; i++)
    {
        cout << sortv[i] << endl;
    }
    //数组
    int sortnums[6];
    for (int i = 0; i < 5; i++)
        cin >> sortnums[i];
    sort(sortnums, sortnums + 5);
    for (int i = 0; i < 5; i++)
        cout << sortnums[i] << endl;
    //此sort是升序排序
    return 0;
}

运行结果：

1 5 4 3 8
1
3
4
5
8
1 5 6 4 8
1
4
5
6
8

怎么把sort函数改成降序呢？
在命名空间下方添加一个函数——cmp（名字任意）

bool cmp(int a, int b)
{
    return a > b;
}

sort函数改成这样

sort(v.begin(), v.end(), cmp);

sort(sortv.begin(), sortv.end());
for (int i = 0; i < 5; i++)
{
cout << sortv[i] << endl;
}
//数组
int sortnums[6];
for (int i = 0; i < 5; i++)
cin >> sortnums[i];
sort(sortnums, sortnums + 5);
for (int i = 0; i < 5; i++)
cout << sortnums[i] << endl;
//此sort是升序排序
return 0;
}

运行结果：

1 5 4 3 8
1
3
4
5
8
1 5 6 4 8
1
4
5
6
8

怎么把sort函数改成降序呢？
在命名空间下方添加一个函数——cmp（名字任意）

```cpp
bool cmp(int a, int b)
{
    return a > b;
}

sort函数改成这样

sort(v.begin(), v.end(), cmp);

就可以了。