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Cplusplus

Comparator in vector C++


I am trying to solve a simple solution for comparing 2 vectors in this post in C++. Let us use STL vectors and std:: equal function to compare. 


There are different ways the comparison can be achieved. 




1. Using the == operator






Example : 




vector<int> first = {2,4,6,8,10};


vector<int> second = {2,4,6,8,10};




Comparing them can be done using ‘==’ operator as follows: 






if (first == second){    std::cout << “The vectors are same” << std::endl;}












The problems with == are 


a. It cannot use custom comparators


b. Cannot compare sub-vector groups 




2. std:: equal can be used to compare 




for equality: 




bool equal (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2);




for predicate: 








bool equal (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, BinaryPredicate pred);











Equality can be used to compare sub vectors: 


Example: 


Comparing all elements can be done by using 






bool isEqual = std::equal(first.begin(),first.end(),second.begin());











Comparing the subset of elements the following can be done.






vector<int> a = {1,2,3,4,5,6};
vector<int> b = {4,5,6}; 


bool isEqual = std::equal( b.begin(),b.end(), a.begin()+2);
if(isEqual)
{
    cout<<"The vectors are equal"<<endl;
}




















































































 














We can use custom comparators. Let’s see how we can do it. 






vector<string> first ={"this", "is", "a", "practise", "of","custom", "comparators"};
vector<string> second ={"THIS", "IS", "A", "PRACTISE", "OF","CUSTOM", "COMPARATORS"};
std::function< bool (const string &, const string & )> comparator = [](const string &left, const string &right)
{
    return std::equal(left.begin(),left.end(),right.begin(),[](const char &l,const char &r){ return ::toupper(l)==::toupper(r))});
}
bool isEqual = std::equal(first.begin(),first.end(),second.begin(),comparator);
if(isEqual)
    cout<<"The strings are same"<<endl; 
else
    cout<<"The strings are not same"<<endl;
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