C++ offers in its STL library a merge() which is quite useful to merge sort two containers into a single container. It is defined in header “algorithm“. It is implemented in two ways. Syntax 1 : Using operator “<”
Template : template outiter merge (initer1 beg1, initer1 end1, initer2 beg2, initer2 end2, outiter res) Parameters : beg1 : Input iterator to initial position of first sequence. end1 : Input iterator to final position of first sequence. beg2 : Input iterator to initial position of second sequence. end2 : Input iterator to final position of second sequence. res : Output Iterator to initial position of resultant container. Return value : Iterator to last element of the resulting container.
CPP
// C++ code to demonstrate the working of // merge() implementation 1 #include <bits/stdc++.h> using namespace std;
int main()
{ // initializing 1st container
vector< int > arr1 = { 1, 4, 6, 3, 2 };
// initializing 2nd container
vector< int > arr2 = { 6, 2, 5, 7, 1 };
// declaring resultant container
vector< int > arr3(10);
// sorting initial containers
sort(arr1.begin(), arr1.end());
sort(arr2.begin(), arr2.end());
// using merge() to merge the initial containers
merge(arr1.begin(), arr1.end(), arr2.begin(), arr2.end(), arr3.begin());
// printing the resultant merged container
cout << "The container after merging initial containers is : ";
for ( int i = 0; i < arr3.size(); i++)
cout << arr3[i] << " ";
return 0;
} |
Output:
The container after merging initial containers is : 1 1 2 2 3 4 5 6 6 7
Syntax 2 : Using comparator function
Template : template outiter merge (initer1 beg1, initer1 end1, initer2 beg2, initer2 end2, outiter res, Compare comp) Parameters : beg1 : Input iterator to initial position of first sequence. end1 : Input iterator to final position of first sequence. beg2 : Input iterator to initial position of second sequence. end2 : Input iterator to final position of second sequence. res : Output Iterator to initial position of resultant container. comp : The comparator function that returns a boolean true/false of the each elements compared. This function accepts two arguments. This can be function pointer or function object and cannot change values. Return value : Iterator to last element of the resulting container.
CPP
// C++ code to demonstrate the working of // merge() implementation 2 #include <bits/stdc++.h> using namespace std;
// comparator function to reverse merge sort struct greaters {
bool operator()( const long & a, const long & b) const
{
return a > b;
}
}; int main()
{ // initializing 1st container
vector< int > arr1 = { 1, 4, 6, 3, 2 };
// initializing 2nd container
vector< int > arr2 = { 6, 2, 5, 7, 1 };
// declaring resultant container
vector< int > arr3(10);
// sorting initial containers
// in descending order
sort(arr1.rbegin(), arr1.rend());
sort(arr2.rbegin(), arr2.rend());
// using merge() to merge the initial containers
// returns descended merged container
merge(arr1.begin(), arr1.end(), arr2.begin(), arr2.end(), arr3.begin(), greaters());
// printing the resultant merged container
cout << "The container after reverse merging initial containers is : ";
for ( int i = 0; i < arr3.size(); i++)
cout << arr3[i] << " ";
return 0;
} |
Output :
The container after reverse merging initial containers is : 7 6 6 5 4 3 2 2 1 1
Possible application : The merge function can be used to make a single stack of two stacks available in sorted order. These can be stack of books or notes. Let us discuss a simple example that merge orders two stack of notes in ascending order into one on basis of its value.
CPP
// C++ code to demonstrate the application of // merge() stacking notes #include <bits/stdc++.h> using namespace std;
int main()
{ // initializing 1st container
// containing denominations
vector< int > stack1 = { 50, 20, 10, 100, 2000 };
// initializing 2nd container
// containing denominations
vector< int > stack2 = { 500, 2000, 10, 100, 50 };
// declaring resultant stack
vector< int > stack3(10);
cout << "The original 1st stack : ";
for ( int i = 0; i < 5; i++)
cout << stack1[i] << " ";
cout << endl;
cout << "The original 2nd stack : ";
for ( int i = 0; i < 5; i++)
cout << stack2[i] << " ";
cout << endl;
// sorting initial stacks of notes
// in descending order
sort(stack1.begin(), stack1.end());
sort(stack2.begin(), stack2.end());
// using merge() to merge the initial stacks
// of notes
merge(stack1.begin(), stack1.end(), stack2.begin(), stack2.end(), stack3.begin());
// printing the resultant stack
cout << "The resultant stack of notes is : ";
for ( int i = 0; i < stack3.size(); i++)
cout << stack3[i] << " ";
return 0;
} |
Output :
The original 1st stack : 50 20 10 100 2000 The original 2nd stack : 500 2000 10 100 50 The resultant stack of notes is : 10 10 20 50 50 100 100 500 2000 2000