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How to Remove Duplicates from an Unsorted Vector while Maintaining Order?
How to Remove Duplicates from an Unsorted Vector while Maintaining Order?
Nov 13, 2024 am 05:59 AM
Removing Duplicates from an Unsorted Vector
Maintaining the order of first occurrences while eliminating duplicates from an unsorted vector is crucial in various situations. While a straightforward approach utilizing a set and manual iteration is effective, it can be improved upon by leveraging STL algorithms.
To achieve this, the std::copy_if algorithm provides a convenient solution. By defining a predicate that keeps track of elements already processed and returns false for duplicates, we can filter out the desired elements.
If C 11 support is unavailable, the clumsily named std::remove_copy_if can be employed, with its logic inverted. Here's an untested example to illustrate:
template <typename T>
struct NotDuplicate {
bool operator()(const T& element) {
return s_.insert(element).second; // true if s_.insert(element);
}
private:
std::set<T> s_;
};
Next, the following code can be used:
std::vector<int> uniqueNumbers;
NotDuplicate<int> pred;
std::copy_if(numbers.begin(), numbers.end(),
std::back_inserter(uniqueNumbers),
std::ref(pred));
In this solution, the std::ref ensures that the stateful functor is not copied internally within the algorithm. However, std::copy_if does not impose any requirements on side-effects of the applied functor.
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