Node* findIntersection(Node *firstHead, Node *secondHead)
{
    unordered_map<Node*,bool>mp;
    while(firstHead)
    {
        mp[firstHead] = 1;
        firstHead = firstHead->next;
    }
    while(secondHead)
    {
        if(mp[secondHead]) return secondHead;
        secondHead = secondHead->next;
    }
    return NULL;
}