算法库| C ++魔术师STL算法

对于所有渴望在竞争性编程中表现出色的人来说，只有不了解STL容器的知识才有用处，直到人们不知道所有STL所提供的内容。
对于所有库函数，STL都有大量的算法：请参阅此处。
以下是一些关于向量的最常用算法和《竞争性编程》中最有用的算法：

非操纵算法

1. sort (first_iterator，last_iterator) –对给定的向量进行排序。
2. reverse(first_iterator，last_iterator) –反转向量。
3. * max_element(first_iterator，last_iterator) –查找向量的最大元素。
4. * min_element(first_iterator，last_iterator) –查找向量的最小元素。
5. accumulate(first_iterator，last_iterator，求和的初始值) –对向量元素求和

CPP

// A C++ program to demonstrate working of sort(),
// reverse()
#include 
#include 
#include 
#include  //For accumulate operation
using namespace std;
 
int main()
{
    // Initializing vector with array values
    int arr[] = {10, 20, 5, 23 ,42 , 15};
    int n = sizeof(arr)/sizeof(arr[0]);
    vector vect(arr, arr+n);
 
    cout << "Vector is: ";
    for (int i=0; i

---

---

输出

Vector is: 10 20 5 23 42 15 
Vector after sorting is: 5 10 15 20 23 42 
Vector after reversing is: 42 23 20 15 10 5 
Maximum element of vector is: 42
Minimum element of vector is: 5
The summation of vector elements is: 115

6.count(first_iterator，last_iterator，x) –计算向量中x的出现。

7. find(first_iterator，last_iterator，x) –如果向量中不存在element，则返回一个迭代器，该迭代器返回向量中x的第一个出现位置，并指向向量的最后一个地址((name_of_vector).end())。

CPP

// C++ program to demonstrate working of count()
// and find()
#include 
#include 
#include 
using namespace std;
 
int main()
{
    // Initializing vector with array values
    int arr[] = {10, 20, 5, 23 ,42, 20, 15};
    int n = sizeof(arr)/sizeof(arr[0]);
    vector vect(arr, arr+n);
 
    cout << "Occurrences of 20 in vector : ";
 
    // Counts the occurrences of 20 from 1st to
    // last element
    cout << count(vect.begin(), vect.end(), 20);
 
    // find() returns iterator to last address if
    // element not present
    find(vect.begin(), vect.end(),5) != vect.end()?
                         cout << "\nElement found":
                     cout << "\nElement not found";
 
    return 0;
}

输出

Occurrences of 20 in vector : 2
Element found

8. binary_search (first_iterator，last_iterator，x) –测试x是否存在于排序的向量中。

9. lower_bound(first_iterator，last_iterator，x) –返回一个迭代器，该迭代器指向[first，last)范围内第一个元素，该元素的值不小于’x’。

10. upper_bound(first_iterator，last_iterator，x) –返回一个迭代器，该迭代器指向[first，last)范围内的第一个元素，该元素的值大于’x’。

C++

// C++ program to demonstrate working of lower_bound()
// and upper_bound().
#include 
#include 
#include 
using namespace std;
 
int main()
{
    // Initializing vector with array values
    int arr[] = {5, 10, 15, 20, 20, 23, 42, 45};
    int n = sizeof(arr)/sizeof(arr[0]);
    vector vect(arr, arr+n);
 
    // Sort the array to make sure that lower_bound()
    // and upper_bound() work.
    sort(vect.begin(), vect.end());
 
    // Returns the first occurrence of 20
    auto q = lower_bound(vect.begin(), vect.end(), 20);
 
    // Returns the last occurrence of 20
    auto p = upper_bound(vect.begin(), vect.end(), 20);
 
    cout << "The lower bound is at position: ";
    cout << q-vect.begin() << endl;
 
    cout << "The upper bound is at position: ";
    cout << p-vect.begin() << endl;
 
    return 0;
}

输出

The lower bound is at position: 3
The upper bound is at position: 5

一些操纵算法

1. arr.erase(要删除的位置) –删除矢量中的选定元素，并相应地移动和调整矢量元素的大小。
2. arr.erase(unique(arr.begin()，arr.end())，arr.end()) –擦除单行中排序向量中的重复项。

CPP

// C++ program to demonstrate working of erase()
#include 
#include 
#include 
using namespace std;
 
int main()
{
    // Initializing vector with array values
    int arr[] = {5, 10, 15, 20, 20, 23, 42, 45};
    int n = sizeof(arr)/sizeof(arr[0]);
    vector vect(arr, arr+n);
 
    cout << "Vector is :";
    for (int i=0; i<6; i++)
        cout << vect[i]<<" ";
 
    // Delete second element of vector
    vect.erase(vect.begin()+1);
 
    cout << "\nVector after erasing the element: ";
    for (int i=0; i<5; i++)
        cout << vect[i] << " ";
 
    // sorting to enable use of unique()
    sort(vect.begin(), vect.end());
 
    cout << "\nVector before removing duplicate "
             " occurrences: ";
    for (int i=0; i<5; i++)
        cout << vect[i] << " ";
 
    // Deletes the duplicate occurrences
    vect.erase(unique(vect.begin(),vect.end()),vect.end());
 
    cout << "\nVector after deleting duplicates: ";
    for (int i=0; i< vect.size(); i++)
        cout << vect[i] << " ";
 
    return 0;
}

输出

Vector is :5 10 15 20 20 23 
Vector after erasing the element: 5 15 20 20 23 
Vector before removing duplicate  occurrences: 5 15 20 20 23 
Vector after deleting duplicates: 5 15 20 23 42 45 

3. next_permutation(first_iterator，last_iterator) –这将向量修改为其下一个排列。

4. prev_permutation(first_iterator，last_iterator) –这将向量修改为其先前的排列。

CPP

// C++ program to demonstrate working
// of next_permutation()
// and prev_permutation()
#include 
#include 
#include 
using namespace std;
 
int main()
{
    // Initializing vector with array values
    int arr[] = {5, 10, 15, 20, 20, 23, 42, 45};
    int n = sizeof(arr)/sizeof(arr[0]);
    vector vect(arr, arr+n);
 
    cout << "Given Vector is:\n";
    for (int i=0; i

输出

Given Vector is:
5 10 15 20 20 23 42 45 
Vector after performing next permutation:
5 10 15 20 20 23 45 42 
Vector after performing prev permutation:
5 10 15 20 20 23 42 45 

5. distance(first_iterator，desired_position) –返回到第一个迭代器的期望位置的距离。此函数在查找索引时非常有用。

CPP

// C++ program to demonstrate working of distance()
#include 
#include 
#include 
using namespace std;
 
int main()
{
    // Initializing vector with array values
    int arr[] = {5, 10, 15, 20, 20, 23, 42, 45};
    int n = sizeof(arr)/sizeof(arr[0]);
    vector vect(arr, arr+n);
 
    // Return distance of first to maximum element
    cout << "Distance between first to max element: ";
    cout << distance(vect.begin(),
                     max_element(vect.begin(), vect.end()));
    return 0;
}

输出

Distance between first to max element: 7

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