forward_list::unique() in C++ STL

forward_list::unique() is an inbuilt function in C++ STL which removes all consecutive duplicate elements from the forward_list. It uses binary predicate for comparison.

Syntax:

forwardlist_name.unique(BinaryPredicate name)

Parameters: The function accepts a single parameter which is a binary predicate that returns true if the elements should be treated as equal.

It has following syntax:

bool name(data_type a, data_type a)

Return value: The function does not return anything. 

CPP

// C++ program to illustrate the
// unique() function
#include <bits/stdc++.h>
using namespace std;

// Function for binary_predicate
/*bool compare(int a, int b)
{
    return (abs(a) == abs(b));
}
// This function can also be used and passed inside
// unique(), to get the same result
*/

int main()
{

    forward_list<int> list = { 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 2, 4, 4 };

    cout << "List of elements before unique operation is: ";

    // starts from the first element of the list to the last
    for (auto it = list.begin(); it != list.end(); ++it)
        cout << *it << " ";

    // unique operation on forward list
    list.unique();
    cout << "\nList of elements after unique operation is: ";

    // starts from the first element of the list to the last
    for (auto it = list.begin(); it != list.end(); ++it)
        cout << *it << " ";

    return 0;
}

Output

List of elements before unique operation is: 1 1 1 1 2 2 2 2 3 3 3 2 4 4 
List of elements after unique operation is: 1 2 3 2 4

Time Complexity: O(N), where N is the number of elements compared

Auxiliary Space: O(1)