Use of C++ set

Use of C++ set

set is also a common container in STL. The set collection container implements a balanced two-fork retrieval tree of red-black trees, which automatically adjusts the arrangement of the two-fork tree to put the elements in place. The set container contains elements whose values are unique to one, and the elements in the collection are arranged in order of one.

We constructed the set collection for quick retrieval, not to modify the key directly.

Some common operations of set:

begin() returns an iterator that points to the first element clear() clears all elements count() returns the number of elements of a value empty() returns true(true) if the set is empty end() returns an iterator that points to the last element, not the last erase() removes elements from the collection find() returns an iterator that points to the element found insert() inserts elements into the collection max_size() returns the maximum value of the elements that the collection can hold The number of elements in the size() collection swap() swaps two set variables

Most of set's operations are similar to vector, except that set does not support random access and must be accessed using an iterator. There is only one insert insert in set, since putting one element into set will adjust the position of the element and put it into the appropriate position.

For a set, we have union, intersection, difference, complement, etc., so we have similar set operations in set, which are all in #include < algorithm > Under the header file:

std::set_intersection() : The function is to find the intersection of two sets.  
std::set_union() : Take the union of two sets  
std::set_difference () : difference set  
std::set_symmetric_difference () : the result is   The first 1 The number of iterators relative to the number 2 A set of difference   And on the first 2 One relative to number one 1 A set of difference  

There is a question on school OJ to do these operations. The following is the question on school OJ:

Description

 The operation of a set is to specify a new set with a given set. set A and B Is a set, then their union difference intersection complement is defined as follows: 
A ∪ B={x|x ∈ A ∨ x ∈ B}
A studying B={x|x ∈ A Sunday afternoon x ∈ B}
A-B={x|x ∈ A Sunday afternoon x Do not belong to  B}
SA ={x|x ∈ (A ∪ B) Sunday afternoon x  Do not belong to A}
SB ={x|x ∈ (A ∪ B) Sunday afternoon x  Do not belong to B}

Input

 The first 1 Line of input 1 A positive integer T So there's a total of T Group test data. ( T<=200 ) 
 And then down here 2T Each line, 1 Lines have n+1 Number one, number two 1 A number is n(0<=n<=100) That means there's more after that bank n Number input. 

Output

 For each set of test data, first output the test data sequence number," Case #.NO ", 
 And then output 7 All right, every line 1 A collection of 
 before 2 Rows output collections separately A , B , take 5 Row to output the collection separately A , B And of the (A u B) , (A n B) Poor, (A  �  B) And repair. 
 The elements in the set are called" {} "Expand, and use between elements,"   "Separated. 

Sample Input

14 1 2 3 10

Sample Output

Case# 1:
A = {1, 2, 3}
B = {}
A u B = {1, 2, 3}
A n B = {}
A - B = {1, 2, 3}
SA = {}
SB = {1, 2, 3}

My code is as follows:

#include<iostream> 
#include<set> 
#include<algorithm> 
#include<vector> 
using namespace std; 
void print(set<int> a) 
{ 
  if(a.begin() == a.end()) 
      cout << "}" << endl; 
  for(set<int>::iterator it = a.begin();it!=a.end();it++) 
  { 
    if(++it==a.end()) 
    { 
      it--; 
      cout << *it << "}\n"; 
    } 
    else 
    { 
      it--; 
      cout << *it << ", "; 
    } 
  } 
} 
int main() 
{ 
  int T, cou = 0; 
  set<int> a, b, c; 
  cin >> T; 
  while(T--) 
  { 
    cou++; 
    a.clear(), b.clear(), c.clear(); 
    int n; 
    cin >> n; 
    for(int i=0;i<n;i++) 
    { 
      int x; 
      cin >> x; 
      a.insert(x); 
    } 
    cin >> n; 
    for(int i=0;i<n;i++) 
    { 
      int x; 
      cin >> x; 
      b.insert(x); 
    } 
    cout << "Case# " << cou << ":" << endl; 
    cout << "A = {"; 
    print(a); 
    cout << "B = {"; 
    print(b); 
    set_union(a.begin(),a.end(),b.begin(),b.end(),inserter(c,c.begin())); 
    cout << "A u B = {"; 
    print(c); 
    c.clear(); 
    set_intersection(a.begin(),a.end(),b.begin(),b.end(),inserter(c,c.begin())); 
    cout << "A n B = {"; 
    print(c); 
    c.clear(); 
    set_difference(a.begin(),a.end(),b.begin(),b.end(),inserter(c,c.begin())); 
    cout << "A - B = {"; 
    print(c); 
    c.clear(); 
    set_difference(b.begin(),b.end(),a.begin(),a.end(),inserter(c,c.begin())); 
    cout << "SA = {"; 
    print(c); 
    c.clear(); 
    set_difference(a.begin(),a.end(),b.begin(),b.end(),inserter(c,c.begin())); 
    cout << "SB = {"; 
    print(c); 
  } 
 
  return 0; 
} 

inserter is an insert iterator in an iterator adapter. Principle: it calls insert() internally

Function: inserts an element at a specified location in a container

Limitation: inserter can only be used in containers that provide the inset() member function. All STL containers provide the inset() function.

Applicable: all STL containers

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