[C + + standard library]_[primary]_[intersection and complement set]

Scene:

1. Calculate the same element in Std::vector A and std::vector B, for the reservation is not deleted.

2. Calculate the respective complement of std::vector A and std::vector B to delete the complement of a and add a complement of B, used in some operations to update the associated table. For example, contact a belongs to Group B is a set of BV, the group of contact a belongs to

To modify the CV of the collection, you need to delete the CV complement set of the two collection BV,CV and the new BV complement.

3. The C + + standard library provides these algorithms for us.

Code:

Test_androidassistant.cpp: Defines the entry point of the console application. #include "stdafx.h" #include <algorithm> #include <vector> #include <string> #include <iostream > #include "gtest/gtest.h" TEST (test_androidassistant,setintersection) {std::vector<int> V1;v1.push_back (3 ); V1.push_back (121), V1.push_back (5);std::vector<int> v2;v2.push_back (2); V2.push_back (); V2.push_back (3); V2.push_back (5); Std::sort (V1.begin (), V1.end ()), Std::sort (V2.begin (), V2.end ());std::vector<int> RESULT;STD :: Set_intersection (V1.begin (), V1.end (), V2.begin (), V2.end (), std::back_inserter (result); Std::cout << "set_ Intersection "<< std::endl;for (int i = 0; i< result.size (); ++i) {std::cout << result[i] << Std::endl; }std::vector<int> d1;std::vector<int> d2;std::cout << "set_different" << std::endl;//copies  The elements from the sorted range [First1, Last1)//which is not found in the sorted range [First2, Last2] to the Range beginning at d_firststd::set_Difference (V1.begin (), V1.end (), Result.begin (), Result.end (), Std::back_inserter (D1)); Std::set_difference ( V2.begin (), V2.end (), Result.begin (), Result.end (), Std::back_inserter (D2)); Std::cout << "Set_difference D1" << std::endl;for (int i = 0; i< d1.size (); ++i) {std::cout << d1[i] << Std::endl;} Std::cout << "Set_difference D2" << std::endl;for (int i = 0; i< d2.size (); ++i) {std::cout << d2[i] &l t;< Std::endl;}} int _tmain (int argc, _tchar* argv[]) {testing::initgoogletest (&AMP;ARGC, argv); Run_all_tests (); return 0;}

Output:

Set_intersection35set_differentset_difference d1121set_difference d2289

Note: Here Std::back_inserter is the creation of the output enumeration type.

Look at the implementation of the set_intersection is very ingenious:

Template<class InputIt1, Class InputIt2, Class Outputit>outputit set_intersection (InputIt1 first1, InputIt1 last1 ,                          InputIt2 first2, InputIt2 last2,                          outputit d_first) {while    (first1! = Last1 && First2! = last2) {
   
    if (*first1 < *first2) {            ++first1;        } else  {            if (! ( *first2 < *first1) {                *d_first++ = *first1++;            }            ++first2;        }    }    return D_first;}
   

And look at the set_difference implementation is ingenious:

Template<class InputIt1, Class InputIt2, Class Outputit>outputit set_difference (InputIt1 first1, InputIt1 last1,< C0/>inputit2 First2, InputIt2 last2,                        outputit d_first) {while    (first1! = last1) {        if (first2 = = Last2) return Std::copy (First1, Last1, D_first);         if (*first1 < *first2) {            *d_first++ = *first1++;        } else {            if (! (*first2 < *first1)) {                ++first1;            }            ++first2;        }    }    return D_first;}

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

[C + + standard library]_[primary]_[intersection and complement set]