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Forward List in C++ | Set 2 (Manipulating Functions)

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Forward List in C++ | Set 1 (Introduction and Important Functions) More functions are discussed in this article Some of the operations other than insertions and deletions that can be used in forward lists are as follows : 

1. merge() :- This function is used to merge one forward list with other. If both the lists are sorted then the resultant list returned is also sorted. 

2. operator “=” :- This operator copies one forward list into other. The copy made in this case is deep copy. 

CPP




// C++ code to demonstrate the working of
// merge() and operator=
#include<iostream>
#include<forward_list>
using namespace std;
 
int main()
{    
    // Initializing 1st forward list
    forward_list<int> flist1 = {1, 2, 3};
     
    // Declaring 2nd forward list
    forward_list<int> flist2;
     
    // Creating deep copy using "="
    flist2 = flist1;
     
    // Displaying flist2
    cout << "The contents of 2nd forward list"
            " after copy are : ";
    for (int &x : flist2)
        cout << x << " ";
    cout << endl;
     
    // Using merge() to merge both list in 1
    flist1.merge(flist2);
     
    // Displaying merged forward list
    // Prints sorted list
    cout << "The contents of forward list "
            "after merge are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl;
     
    return 0;    
}


Output:

The contents of 2nd forward list after copy are : 1 2 3 
The contents of forward list after merge are : 1 1 2 2 3 3 

Time Complexity: O(1)

Auxiliary Space: O(1)
 3. sort() :- This function is used to sort the forward list. 

4. unique() :- This function deletes the multiple occurrences of a number and returns a forward list with unique elements. The forward list should be sorted for this function to execute successfully. 

CPP




// C++ code to demonstrate the working of
// sort() and unique()
#include<iostream>
#include<forward_list> // for sort() and unique()
using namespace std;
 
int main()
{
    // Initializing 1st forward list
    forward_list<int> flist1 = {1, 2, 3, 2, 3, 3, 1};
 
    // Sorting the forward list using sort()
    flist1.sort();
 
    // Displaying sorted forward list
    cout << "The contents of forward list after "
            "sorting are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl;
 
    // Use of unique() to remove repeated occurrences
    flist1.unique();
 
    // Displaying forward list after using unique()
    cout << "The contents of forward list after "
            "unique operation are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl;
 
    return 0;
}


Output:

The contents of forward list after sorting are : 1 1 2 2 3 3 3 
The contents of forward list after unique operation are : 1 2 3 

Time Complexity: O(1)

Auxiliary Space: O(1)
 

5. reverse() :- This function is used to reverse the forward list.

6. swap() :- This function swaps the content of one forward list with other. 

CPP




// C++ code to demonstrate the working of
// reverse() and swap()
#include<iostream>
#include<forward_list> // for reverse() and swap()
using namespace std;
int main()
{
    // Initializing 1st forward list
    forward_list<int> flist1 = {1, 2, 3,};
 
    // Initializing 2nd forward list
    forward_list<int> flist2 = {4, 5, 6};
 
    // Using reverse() to reverse 1st forward list
    flist1.reverse();
 
    // Displaying reversed forward list
    cout << "The contents of forward list after"
            " reversing are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl << endl;
 
    // Displaying forward list before swapping
    cout << "The contents of 1st forward list "
            "before swapping are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl;
    cout << "The contents of 2nd forward list "
            "before swapping are : ";
    for (int &x : flist2)
        cout << x << " ";
    cout << endl;
 
    // Use of swap() to swap the list
    flist1.swap(flist2);
 
    // Displaying forward list after swapping
    cout << "The contents of 1st forward list "
            "after swapping are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl;
 
    cout << "The contents of 2nd forward list "
            "after swapping are : ";
    for (int &x : flist2)
        cout << x << " ";
    cout << endl;
 
    return 0;
}


Output:

The contents of forward list after reversing are : 3 2 1 

The contents of 1st forward list before swapping are : 3 2 1 
The contents of 2nd forward list before swapping are : 4 5 6 
The contents of 1st forward list after swapping are : 4 5 6 
The contents of 2nd forward list after swapping are : 3 2 1 

Time Complexity: O(1)

Auxiliary Space: O(1)
 

7. clear() :- This function clears the contents of forward list. After this function, the forward list becomes empty.

 8. empty() :- This function returns true if the list is empty otherwise false. 

CPP




// C++ code to demonstrate the working of
// clear() and empty()
#include<iostream>
#include<forward_list> // for clear() and empty()
using namespace std;
int main()
{    
    // Initializing forward list
    forward_list<int> flist1 = {1, 2, 3,};
     
    // Displaying forward list before clearing
    cout << "The contents of forward list are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl;
     
    // Using clear() to clear the forward list
    flist1.clear();
     
    // Displaying list after clear() performed
    cout << "The contents of forward list after "
        << "clearing are : ";
    for (int &x : flist1)
        cout << x << " ";
    cout << endl;
     
    // Checking if list is empty
    flist1.empty() ? cout << "Forward list is empty" :
                    cout << "Forward list is not empty";
     
    return 0;    
}


Output:

The contents of forward list  are : 1 2 3 
The contents of forward list after clearing are : 
Forward list is empty

Time Complexity: O(1)

Auxiliary Space: O(1)
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Last Updated : 21 Jun, 2022
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