算法库（C++魔术师STL算法用法示例）

本文概述

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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, 直到人们不知道所有STL所提供的内容。
STL有大量的算法, 可用于所有< algorithm> 库函数：请参见
这里
.
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

分类(first_iterator, last_iterator)–对给定向量进行排序。
反向(first_iterator, last_iterator)–反转向量。
* max_element(first_iterator, last_iterator)–查找向量的最大元素。
* min_element(first_iterator, last_iterator)–查找向量的最小元素。
累积(first_iterator, last_iterator, 总和的初始值)–是否对向量元素求和

CPP

// A C++ program to demonstrate working of sort(), // reverse() #include < algorithm> #include < iostream> #include < vector> #include < numeric> //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< int > vect(arr, arr+n); cout < < "Vector is: " ; for ( int i=0; i< n; i++) cout < < vect[i] < < " " ; // Sorting the Vector in Ascending order sort(vect.begin(), vect.end()); cout < < "\nVector after sorting is: " ; for ( int i=0; i< n; i++) cout < < vect[i] < < " " ; // Reversing the Vector reverse(vect.begin(), vect.end()); cout < < "\nVector after reversing is: " ; for ( int i=0; i< 6; i++) cout < < vect[i] < < " " ; cout < < "\nMaximum element of vector is: " ; cout < < *max_element(vect.begin(), vect.end()); cout < < "\nMinimum element of vector is: " ; cout < < *min_element(vect.begin(), vect.end()); // Starting the summation from 0 cout < < "\nThe summation of vector elements is: " ; cout < < accumulate(vect.begin(), vect.end(), 0); return 0; }

输出如下

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.查找(first_iterator, last_iterator, x)
–如果向量中不存在元素, 则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 < algorithm> #include < iostream> #include < vector> 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< int > 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; }

输出如下

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 < algorithm> #include < iostream> #include < vector> 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< int > 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; }

输出如下

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

一些操纵算法

arr.erase(要删除的位置)–这将擦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。
arr.erase(唯一(arr.begin(), arr.end()), arr.end())–这会擦除单行中排序向量中的重复出现。

CPP

// C++ program to demonstrate working of erase() #include < algorithm> #include < iostream> #include < vector> 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< int > 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; }

输出如下

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

【算法库（C++魔术师STL算法用法示例）】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 < algorithm> #include < iostream> #include < vector> 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< int > vect(arr, arr+n); cout < < "Given Vector is:\n" ; for ( int i=0; i< n; i++) cout < < vect[i] < < " " ; // modifies vector to its next permutation order next_permutation(vect.begin(), vect.end()); cout < < "\nVector after performing next permutation:\n"; for ( int i=0; i< n; i++) cout < < vect[i] < < " " ; prev_permutation(vect.begin(), vect.end()); cout < < "\nVector after performing prev permutation:\n"; for ( int i=0; i< n; i++) cout < < vect[i] < < " " ; return 0; }

输出如下

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.距离(first_iterator, 期望位置)–它返回到第一个迭代器的期望位置的距离。此功能在查找索引时非常有用。
CPP

// C++ program to demonstrate working of distance() #include < algorithm> #include < iostream> #include < vector> 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< int > 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; }

输出如下

Distance between first to max element: 7

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本文作者：
Manjeet Singh。
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