Check std::vector has duplicates

Question

I want to check if a vector of integers has any duplicates or not, and have to return true if it does. So I try to do something like this:

vector<int> uGuess = {1,2,3,3,4,5}
vector<int> a = uGuess;
sort(a.begin(), a.end());
bool d = unique(a.begin(), a.end());

And this will not work since unqiue cannot be assigned as a bool value. How should I proceed towards this? If I were to write a for loop to perform the same action, how should I do that?

Answer 1

The algorithm you're looking for is std::adjacent_find.

// The container must be sorted!
const std::vector<int> sortedVector = {1,2,3,3,4,5};
const bool hasDuplicates = std::adjacent_find(sortedVector.begin(), sortedVector.end()) != sortedVector.end();

Unlike std::unique, std::adjacent_find doesn't modify the container.

As a bonus, std::adjacent_find returns an iterator to the first element in the duplicate "pair":

const auto duplicate = std::adjacent_find(sortedVector.begin(), sortedVector.end());

if (duplicate != sortedVector.end())
    std::cout << "Duplicate element = " << *duplicate << "\n";