Compare vector of pair!

Question

I have a vector of pair i.e., vector<pair<int,int>>graph; which has data like this:
1 0
2 1
1 2
3 2
I want to make adjacency list like :
( 1, 0) -> ( 2, 1) ( 1, 2)
( 2, 1) -> ( 1, 0) ( 1, 2)
( 1, 2) -> ( 1, 0) ( 2, 1) ( 1, 2)
( 3, 2) -> ( 2, 1) (1, 2)
If one of the element of pair is a part of second pair. It should be a part of adjacency list.
I tried this,
vector<pair<int,int>>graph2(totalnode);

while (input >> node1 >> node2)
{
graph2.push_back(make_pair(node1,node2));
}

vector<pair<int,int>>::iterator firstloop;
vector<pair<int, int>>::iterator secondloop;
for(firstloop = graph2.begin();firstloop != graph2.end(); firstloop++)
{
for (secondloop = graph2.begin(); secondloop != graph2.end(); secondloop++)
{
if (graph2[firstloop].first == graph2[secondloop].first || graph2[firstloop].first == graph2[secondloop].second
|| graph2[firstloop].second == graph2[secondloop].first || graph2[firstloop].second == graph2[secondloop].second)
{

}
}
}

But this is not right, what can I do for that.
And once I found the matching element, where do I save it ( in another vector of pair?).

Answer 1

How is this a vector/list? Looks like a map of pair to list of pairs or std::multimap.
Is (1, 0) mapped to a list of (2, 1) (1, 2)?
Why not use a matrix?