删除std :: map中的元素的不同方法(erase()和clear())

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📜 删除std :: map中的元素的不同方法(erase()和clear())

📅 最后修改于: 2021-05-30 08:27:43 🧑 作者: Mango

本文介绍了Maps的删除部分。

使用擦除() ：擦除()用于擦除参数中提到的映射中的对，无论是其位置，其值还是数字范围。

delete(key) ：使用其参数中提到的key擦除键值对。删除后重新排序地图。它返回删除的条目数。如果删除了不存在的密钥，则返回0。
时间复杂度： log(n) (n是地图的大小)
delete(iter) ：在参数中提到的迭代器指向的位置擦除该对。
时间复杂度： log(n) (n是地图的大小)
delete(strt_iter，end_iter) ：擦除从“ strt_iter”到“ end_iter”的成对范围。
时间复杂度： O(k) (k是地图的大小)

// C++ code to demonstrate the working of erase()
  
#include
#include // for map operations
using namespace std;
  
int main()
{
    // declaring map
    // of char and int
    map< char, int > mp;
      
    // declaring iterators
    map::iterator it ;
    map::iterator it1;
    map::iterator it2;
      
    // inserting values 
    mp['a']=5;
    mp['b']=10;
    mp['c']=15;
    mp['d']=20;
    mp['e']=30;
  
    // printing initial map elements
    cout << "The initial map elements are : \n";
      
    for (it1 = mp.begin(); it1!=mp.end(); ++it1)
        cout << it1->first << "->" << it1->second << endl;
      
    it = mp.begin();
      
    cout << endl;
      
    // erasing element using iterator
    // erases 2nd element
    // 'b'
    ++it;
    mp.erase(it);
      
    // printing map elements after deletion
    cout << "The map elements after 1st deletion are : \n";
      
    for (it1 = mp.begin(); it1!=mp.end(); ++it1)
        cout << it1->first << "->" << it1->second << endl;
      
    cout << endl;
      
    // erasing element using value 
    int c = mp.erase('c');
      
    // printing map elements after deletion
    cout << "The map elements after 2nd deletion are : \n";
      
    for (it1 = mp.begin(); it1!=mp.end(); ++it1)
        cout << it1->first << "->" << it1->second << endl;
      
    cout << "The number of elements deleted in 2nd deletion are : ";
    cout << c << endl;
      
    cout << endl;
      
    // erasing element using value 
    // key not present
    int d = mp.erase('w');
      
    // printing map elements after deletion
    cout << "The map elements after 3rd deletion are : \n";
      
    for (it1 = mp.begin(); it1!=mp.end(); ++it1)
        cout << it1->first << "->" << it1->second << endl;
      
    cout << "The number of elements deleted in 3rd deletion are : ";
    cout << d << endl;
      
    cout << endl;
      
      
    ++it;
    ++it;
      
    // erasing element using range iterator
    // deletes "d" and "e" keys
    mp.erase(it, mp.end());
      
    // printing map elements 4th deletion
    cout << "The map elements after 4th deletion are : \n";
  
    for (it1 = mp.begin(); it1!=mp.end(); ++it1)
        cout << it1->first << "->" << it1->second << endl;
      
    cout << endl;
      
}

输出：

The initial map elements are : 
a->5
b->10
c->15
d->20
e->30

The map elements after 1st deletion are : 
a->5
c->15
d->20
e->30

The map elements after 2nd deletion are : 
a->5
d->20
e->30
The number of elements deleted in 2nd deletion are : 1

The map elements after 3rd deletion are : 
a->5
d->20
e->30
The number of elements deleted in 3rd deletion are : 0

The map elements after 4th deletion are : 
a->5

使用clear() ：此函数清除地图中存在的所有元素。调用此函数后，映射的大小变为0。

// C++ code to demonstrate the working of clear()
  
#include
#include // for map operations
using namespace std;
  
int main()
{
    // declaring map
    // of char and int
    map< char, int > mp;
      
    // declaring iterator
    map::iterator it ;
      
    // inserting values 
     mp['a']=5;
     mp['b']=10;
     mp['c']=15;
     mp['d']=20;
     mp['e']=30;
  
    // printing initial map elements
    cout << "The initial map elements are : \n";
    for (it1 = mp.begin(); it1!=mp.end();  ++it1)
    cout << it1->first << "->" << it1->second << endl;
      
    // using clear() to erase all elements in map
    mp.clear();
      
    // printing map elements after deletion
    cout << "The map elements after clearing all elements are : \n";
    for (it1 = mp.begin(); it1!=mp.end();  ++it1)
    cout << it1->first << "->" << it1->second << endl;
      
}

输出：

The initial map elements are : 
a->5
b->10
c->15
d->20
e->30
The map elements after clearing all elements are :

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