C++ List Library - unique() Function

Description

The C++ function std::list::unique() Removes all consecutive duplicate elements from the list. It uses binary predicate for comparison.

Declaration

Following is the declaration for std::list::unique() function form std::list header.

C++98

template <class BinaryPredicate>
void unique (BinaryPredicate binary_pred);

Parameters

binary_pred − binary predicate which returns true if the elements should be treated as equal. It has following prototype.

bool pred(const Type1 &arg1, const Type2 &arg2);

Return value

None

Exceptions

This member function never throws exception.

Time complexity

Linear i.e. O(n)

Example

The following example shows the usage of std::list::unique() function.

#include <iostream>
#include <list>

using namespace std;

/* Ignore sign of the value */
bool pred(int a, int b) {
   return (abs(a) == abs(b));
}

int main(void) {
   list <int> l = {1, -1, -1, -1, 2, 2, -2, -2, 3, -4, 4, -5, -5, 5};

   cout << "List elements before unique operation" << endl;

   for (auto it = l.begin(); it != l.end(); ++it)
      cout << *it << endl;

   /* Ignore sign of the value */
   l.unique(pred);

   cout << "List elements after unique operation" << endl;

   for (auto it = l.begin(); it != l.end(); ++it)
      cout << *it << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

List elements before unique operation
1
-1
-1
-1
2
2
-2
-2
3
-4
4
-5
-5
5
List elements after unique operation
1
2
3
-4
-5