C++ set rbegin()函数用于返回反向迭代器,引用了set集合的最后一个元素。
set的反向迭代器沿相反方向移动,并递增直到到达set集合的开头(第一个元素)。
reverse_iterator rbegin(); //until C++ 11 const_reverse_iterator rbegin() const; //until C++ 11 reverse_iterator rbegin() noexcept; //since C++ 11 const_reverse_iterator rbegin() const noexcept; //since C++ 11
它返回反向的迭代器(reverse iterator),该迭代器指向集合的最后一个元素。
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让我们看一下rbegin()函数的简单示例:
#include <iostream> #include <set> using namespace std; int main () { set<int> myset= {10,50,30,40,20}; //show content: cout<<"Elements are: "<<endl; set<int>::reverse_iterator rit; for (rit=myset.rbegin(); rit!=myset.rend(); ++rit) cout << *rit<< '\n'; return 0; }
输出:
Elements are: 50 40 30 20 10
在上面的示例中,rbegin()函数用于返回指向myset集合中最后一个元素的反向迭代器。
因为集合因此按键的排序顺序存储元素,所以对集合进行迭代将导致上述顺序,即键的排序顺序。
让我们看一个简单的示例,使用while循环以相反的顺序遍历集合:
#include <iostream> #include <set> #include <string> #include <iterator> using namespace std; int main() { // Creating & Initializing a set of String set<string> setEx = {"aaa", "ccc", "ddd", "bbb"}; // Create a set iterator and point to the end of set set<string, int>::reverse_iterator it = setEx.rbegin(); // Iterate over the set using Iterator till beginning. while (it != setEx.rend()) { // Accessing KEY from element pointed by it. string word = *it; cout << word << endl; // Increment the Iterator to point to next entry it++; } return 0; }
输出:
ddd ccc bbb aaa
在上面的示例中,我们使用while循环以相反的顺序迭代集合,并使用rbegin()函数初始化集合的最后一个元素。
因为集合因此按键的排序顺序存储元素,所以对集合进行迭代将导致上述顺序,即键的排序顺序。
让我们看一个简单的示例,以获取反转集的第一个元素:
#include <set> #include <iostream> int main( ) { using namespace std; set <int> s1; set <int>::iterator s1_Iter; set <int>::reverse_iterator s1_rIter; s1.insert( 10 ); s1.insert( 20 ); s1.insert( 30 ); s1_rIter = s1.rbegin( ); cout << "The first element in the reversed set is " << *s1_rIter << "." << endl; //begin can be used to start an iteration //throught a set in a forward order cout << "The set is:"; for ( s1_Iter = s1.begin( ) ; s1_Iter != s1.end( ); s1_Iter++ ) cout << " " << *s1_Iter; cout << endl; //rbegin can be used to start an iteration //throught a set in a reverse order cout << "The reversed set is:"; for ( s1_rIter = s1.rbegin( ) ; s1_rIter != s1.rend( ); s1_rIter++ ) cout << " " << *s1_rIter; cout << endl; //A set element can be erased by dereferencing to its key s1_rIter = s1.rbegin( ); s1.erase ( *s1_rIter ); s1_rIter = s1.rbegin( ); cout << "After the erasure, the first element " << "in the reversed set is "<< *s1_rIter << "." << endl; return 0; }
输出:
The first element in the reversed set is 30. The set is: 10 20 30 The reversed set is: 30 20 10 After the erasure, the first element in the reversed set is 20.
让我们看一个简单的示例来对最高分进行排序和计算:
#include <iostream> #include <string> #include <set> using namespace std; int main () { set<int> marks = {400, 350, 465, 290, 410}; cout << "Marks" << '\n'; cout<<"______________________\n"; set<int>::reverse_iterator rit; for (rit=marks.rbegin(); rit!=marks.rend(); ++rit) cout << *rit<< '\n'; auto ite = marks.rbegin(); cout << "\nHighest Marks is: "<< *ite <<" \n"; return 0; }
输出:
Marks ______________________ 465 410 400 350 290 Highest Marks is: 465
在以上示例中,实现了以标记为键的设置标记。这使我们能够利用自动分类的优势并识别最高分数。
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