# remove duplicates from vector c with code examples

Removing duplicates from a vector in C++ can be done in a variety of ways. One common method is to use the STL (Standard Template Library) algorithm 'unique', which removes all consecutive duplicate elements in a range. Another method is to use a combination of STL algorithms 'sort' and 'erase'.

Here is an example of using the 'unique' algorithm to remove duplicates from a vector:

```#include <iostream>
#include <vector>
#include <algorithm>

int main()
{
std::vector<int> v = {1, 2, 2, 3, 4, 4, 5};
std::vector<int>::iterator it;

// Removing duplicates
it = std::unique(v.begin(), v.end());
v.resize(std::distance(v.begin(), it));

// Printing the vector
for (int x : v)
std::cout << x << " ";
return 0;
}
```

Output:

```1 2 3 4 5
```

Here is an example of using the 'sort' and 'erase' algorithm to remove duplicates from a vector:

```#include <iostream>
#include <vector>
#include <algorithm>

int main()
{
std::vector<int> v = {1, 2, 2, 3, 4, 4, 5};

// Sorting the vector
std::sort(v.begin(), v.end());

// Removing duplicates
v.erase(std::unique(v.begin(), v.end()), v.end());

// Printing the vector
for (int x : v)
std::cout << x << " ";
return 0;
}
```

Output:

```1 2 3 4 5
```

Both of the above examples use similar approach to remove duplicates from vector. The first example uses 'unique' algorithm which removes all consecutive duplicate elements from the range and the second example uses 'sort' and 'erase' algorithm to remove duplicates.

Both methods have their own advantages and disadvantages. The 'unique' algorithm modifies the original vector in-place and preserves the order of the elements while the 'sort' and 'erase' method sorts the vector first before removing the duplicates.

In both of the examples, the resulting vector contains only unique elements, with all duplicates removed. One can choose any of these methods based on the specific requirements of the program.

Another method for removing duplicates from a vector in C++ is to use a hash set. A hash set is a container that stores unique elements, and can be used to quickly check if an element already exists in the set. Here's an example of using a hash set to remove duplicates from a vector:

```#include <iostream>
#include <vector>
#include <unordered_set>

int main()
{
std::vector<int> v = {1, 2, 2, 3, 4, 4, 5};
std::unordered_set<int> set;

// Removing duplicates
for (int x : v) {
set.insert(x);
}

// Clearing the vector
v.clear();

// Copying the elements from set to vector
for (int x : set) {
v.push_back(x);
}

// Printing the vector
for (int x : v)
std::cout << x << " ";
return 0;
}
```

Output:

```1 2 3 4 5
```

This method first creates an unordered_set and then iterates through the vector, inserting each element into the set. Because a set only stores unique elements, any duplicates in the vector will not be added to the set. Next, the original vector is cleared and the elements from the set are copied back into the vector, resulting in a vector that only contains unique elements.

This method also has its own advantages and disadvantages. It uses additional memory to store the set and it changes the order of the elements but it allows for fast checking if an element already exists in the set, making it suitable for large and dynamic input.

Another way to remove duplicates from a vector is by using a custom comparator function. With this method, you can define a custom function that compares elements in the vector and removes duplicates based on the comparison. Here's an example of using a custom comparator function to remove duplicates:

```#include <iostream>
#include <vector>
#include <algorithm>

bool compare(int a, int b) {
return a == b;
}

int main()
{
std::vector<int> v = {1, 2, 2, 3, 4, 4, 5};

// Removing duplicates
v.erase(std::unique(v.begin(), v.end(), compare), v.end());

// Printing the vector
for (int x : v)
std::cout << x << " ";
return 0;
}
```

Output:

```1 2 3 4 5
```

This method uses the STL algorithm 'unique' with a custom comparator function, which is passed as the third argument. In this example, the comparator function compares two integers and returns true if they are equal, indicating that they are duplicates.

In conclusion, there are various ways to remove duplicates from a vector in C++, each with its own advantages and disadvantages. The choice of method will depend on the specific requirements of the program, such as memory usage, performance, and the order of the elements in the vector.

## Popular questions

1. What is the simplest method for removing duplicates from a vector in C++?
• The simplest method for removing duplicates from a vector in C++ is to use the STL algorithm 'unique', which removes consecutive duplicates from the vector.
1. How can a hash set be used to remove duplicates from a vector in C++?
• A hash set can be used to remove duplicates from a vector in C++ by first creating an unordered_set, then iterating through the vector, inserting each element into the set. Because a set only stores unique elements, any duplicates in the vector will not be added to the set. Next, the original vector is cleared and the elements from the set are copied back into the vector, resulting in a vector that only contains unique elements.
1. What is the advantage of using a hash set over the 'unique' algorithm?
• The advantage of using a hash set over the 'unique' algorithm is that it allows for fast checking if an element already exists in the set, making it suitable for large and dynamic input.
1. What is a custom comparator function and how can it be used to remove duplicates from a vector?
• A custom comparator function is a function that compares elements in the vector and removes duplicates based on the comparison. It can be used to remove duplicates from a vector by passing it as the third argument to the STL algorithm 'unique'. In this example, the comparator function compares two integers and returns true if they are equal, indicating that they are duplicates.
1. What are the main factors to consider when choosing a method for removing duplicates from a vector in C++?
• The main factors to consider when choosing a method for removing duplicates from a vector in C++ are memory usage, performance, and the order of the elements in the vector. Depending on the specific requirements of the program, one method may be more suitable than others.

### Tag

Deduplication

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