Set union algorithm using vector in C++

Question

I'm only using std::vector in this problem, and I can guarantee no duplicates in each vector (but there isn't any order in each vector). How do I union the vectors I have?

Example:

If I have following vectors...

1
1
3 2
5
5 4
2
4
4 2

After the union I should have only two vectors left:

1
2 3 4 5

Again I'm only using vector, std::set isn't allowed.

Solution 1

You can use std::set_union algorithm.

int first[] = {5,10,15,20,25};
  int second[] = {50,40,30,20,10};
  std::vector<int> v(10);                      // 0  0  0  0  0  0  0  0  0  0
  std::vector<int>::iterator it;

  std::sort (first,first+5);     //  5 10 15 20 25
  std::sort (second,second+5);   // 10 20 30 40 50

  it=std::set_union (first, first+5, second, second+5, v.begin());
                                               // 5 10 15 20 25 30 40 50  0  0
  v.resize(it-v.begin());                      // 5 10 15 20 25 30 40 50

Refer :http://www.cplusplus.com/reference/algorithm/set_union/

Solution 2

Sort the vectors, then merge them like in mergesort, but don't insert duplicates.

vector<int> a, b, c;
sort( a.begin(), a.end());
sort( b.begin(), b.end());
int i = 0, j = 0;
while( i < a.size() && j < b.size())
if( a[ i ] == b[ j ] )
{
   c.push_back( a[ i ] );
   ++i, ++j;
}
else if( a[ i ] < b[ j ] )
   c.push_back( a[ i++ ] );
else 
   c.push_back( b[ j++ ] );

while( i < a.size()) c.push_back( a[ i++ ] );
while( j < b.size()) c.push_back( b[ j++ ] );