How do STL Algorithms Help Remove Duplicates from an Unsorted Vector?

Removing Duplicates from Unsorted Vectors: A Stroll with STL Algorithms

When faced with the task of weeding out duplicate elements from an unsorted vector while preserving the initial ordering, it's tempting to embark on an iterative approach, tediously tracking and removing unwanted entries. But hold on, there's a better way—a path paved with STL algorithms.

The STL Ladder to Duplicate Removal

STL boasts a potent arsenal of algorithms, including std::copy_if, meticulously designed for such scenarios. This magic potion takes an iterable source (like your vector), a destination (where you want the duplicates to vanish), and a predicate to guide the selection process.

Crafting the Duplicate Detector

The key to unlocking std::copy_if's prowess lies in crafting a custom predicate that sniffs out duplicates. Here, we introduce NotDuplicate—a function object that eagerly inserts elements into a set and employs the sacred principle that "a set can't hold 'em all." It gracefully returns false when an element has been encountered before.

The Algorithm's Swift Swipe

With our trusty NotDuplicate predicate in hand, we can invoke std::copy_if to elegantly traverse our vector. Each element is presented to NotDuplicate, which consults its set of seen elements and only grants passage to bona fide newcomers. The unique survivors glide into the destination container, leaving the duplicates to perish in the digital void.

A Peek into the Code's Grace

Let's peek behind the scenes of our elegant solution:

std::vector<int> uniqueNumbers;
NotDuplicate<int> pred;
std::copy_if(numbers.begin(), numbers.end(),
             std::back_inserter(uniqueNumbers),
             std::ref(pred));

This pristine code snippet summons NotDuplicate to assist std::copy_if, swiftly sifting through your vector and weaving a new duplicate-free tapestry.

In C 11's Embrace

If you're blessed with the sweet embrace of C 11, you can unleash the captivating power of lambdas and adorn your code with a touch of succinct elegance:

std::vector<int> uniqueNumbers;
std::copy_if(numbers.begin(), numbers.end(),
             std::back_inserter(uniqueNumbers),
             [](const int& element) {
                return s_.insert(element).second; // true if s_.insert(element);
             });

The Takeaway: Algorithms, Your Stalwart Allies

Remember, the purpose of STL algorithms is not to turn you into an algorithm wizard but to augment your programming prowess. Embrace their rich tapestry of functionality, and you'll find yourself unlocking the full potential of your code with ease and efficiency.

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