Vector Merge Algorithm C++ - c++

Question

Having a hard time designing an efficient algorithm that accomplishes the following. If I start with a 2d vector A,
A = [1 2 3;
2 3 4;
5 6]
I want to take the rows that contain common elements and combine them (removing duplicates) resulting in 2d vector B:
B = [1 2 3 4;
5 6]
I can accomplish this in Matlab, but am having a hard time in C++. Any help is appreciated.

Answer 1

Try this, it worked for me with your example matrix. It looks like a lot of code, but there are functions just for the example and for debugging purpose.
void disp( const std::vector< int >& a )
{
for ( const auto item : a )
{
std::cout << item;
}
std::cout << "\n";
}
void disp( const std::vector< std::vector< int > >& matrix )
{
for ( const auto& row : matrix )
{
disp( row );
}
}
// I think there shall be some easier way for this.
bool hasCommonElements( const std::vector< int >& aVector1, const std::vector< int >& aVector2 )
{
for ( const auto item1 : aVector1 )
{
for ( const auto item2 : aVector2 )
{
if ( item1 == item2 )
{
return true;
}
}
}
return false;
}
void makeAllElementsUnique( std::vector< int >& aRow )
{
std::sort( aRow.begin(), aRow.end() );
aRow.erase( std::unique( aRow.begin(), aRow.end() ), aRow.end() );
}
void mergeRowsWithCommonValues( std::vector< std::vector< int > >& aMatrix )
{
for ( auto it = aMatrix.begin(); it != aMatrix.end(); ++it )
{
auto it2 = it + 1;
while ( it2 != aMatrix.end() )
{
if ( hasCommonElements( *it, *it2 ) )
{
(*it).insert( (*it).end(), (*it2).begin(), (*it2).end() ); // Merge the rows with the common value(s).
makeAllElementsUnique( (*it) );
it2 = aMatrix.erase( it2 ); // Remove the merged row.
}
else
{
++it2;
}
}
}
}
void example()
{
std::vector< std::vector< int > > matrix;
matrix.push_back( { 1, 2, 3 } );
matrix.push_back( { 2, 3, 4 } );
matrix.push_back( { 5, 6 } );
disp( matrix );
mergeRowsWithCommonValues( matrix );
disp( matrix );
}

Answer 2

Here is my own attempt, kinda messy, I know.
int index2 = 0;
int rowIndex = 0;
int tracker = 0;
int insert = 0;
// Loop over all rows
while (index2 < A.size()){
// Check if vector is empty. If so, copy the first row in.
if (B.empty()){
B.push_back(A[index2]);
index2++;
cout<<"Hit an empty.\n";
}
// If vector not empty, do the complicated stuff.
else if (!B.empty()){
for (int i = 0; i < A[index2].size(); i++){ // element in A
for (int j = 0; j < B.size(); j++){ // row in B
for (int k = 0; k < B[j].size(); k++){ // element in row in B
if (A[index2][i] == B[j][k]){
rowIndex = j;
tracker = 1;
}
}
}
}
// If tracker activated, we know there's a common element.
if (tracker == 1){
cout<<"Hit a positive tracker.\n";
for (int i = 0; i < A[index2].size(); i++){ // element in A
for (int j = 0; j < B[rowIndex].size(); j++){ // element in B at rowIndex
if (A[index2][i] != B[rowIndex][j])
insert++;
cout<<"Hit an insert increment.\n";
}
if (insert == B[rowIndex].size()){
cout<<"Hit an insert.\n";
B[rowIndex].push_back(A[index2][i]);
}
insert = 0;
}
index2++;
}else{
B.push_back(A[index2]);
index2++;
cout<<"Hit a zero tracker.\n";
}
}
tracker = 0;
}