CODEWITHSUNDEEP
c++vectorstlunique
Juanti
Juanti

Reputation: 75

Determine if there are duplicates in vector

I would like to determine if there are duplicates in a vector. What is the best option here?

sort(arrLinkToClients.begin(), arrLinkToClients.end(), [&](const type1& lhs,const type1& rhs)
{
    lhs.nTypeOfLink < rhs.nTypeOfLink;
});

auto it = unique(arrLinkToClients.begin(), arrLinkToClients.end(), [&](const type1& lhs, const type1& rhs)
{
    lhs.nTypeOfLink == rhs.nTypeOfLink;
});

//how to check the iterator if there are duplicates ?
if (it)
{
  //
}

Upvotes: 1

Views: 4444

Answers (2)

bolov
bolov

Reputation: 75698

The "best" option does not exist. It depends on how you define "best".

Here are some solutions, each with their own advantages and disadvantages:

Using map 
template <class T>
auto has_duplicates(const std::vector<T>& v) -> bool
{
    std::unordered_map<T, int> m;

    for (const auto& e : v)
    {
        ++m[e];

        if (m[e] > 1)
            return true;
    }
    return false;
}
Using set 
template <class T>
auto has_duplicates(const std::vector<T>& v) -> bool
{
    std::unordered_set<int> s;
    std::copy(v.begin(), v.end(), std::inserter(s, s.begin());
   
    return v.size() != s.size();
}
Using sort and adjacent_find (mutating range) 
template <class T>
auto has_duplicates(std::vector<T>& v) -> bool
{
    std::sort(v.begin(), v.end());

    return std::adjacent_find(v.begin(), v.end()) != v.last();
}
Manual iteration with std::find 
template <class T>
auto has_duplicates(const std::vector<T>& v) -> bool
{
    for (auto it = v.begin(); it != v.end(); ++it)
        if (std::find(it + 1, v.end(), *it) != v.end())
            return true;
            
    return false;
}
Manual iteration 
template <class T>
auto has_duplicates(const std::vector<T>& v) -> bool
{
    for (auto i1 = v.begin(); i1 != v.end(); ++i1)
        for (auto i2 = i1 + 1; i2 != v.end(); ++i2)
            if (*i1 == *i2)
                return true;
    
    return false;
}

Upvotes: 6

jrok
jrok

Reputation: 55395

If there are no duplicates, the iterator returned from unique is the end iterator. So:

if (it != arrLinkToClients.end())
    cout << "Some duplicates found!";

Upvotes: 1

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