Intersection of Two Linked Lists

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        unordered_set<ListNode *>s;
        while(headA!=NULL){
            s.insert(headA);
            headA=headA->next;
        
        
        }
        while(headB!=NULL){
            if(s.find(headB)!=s.end())return headB;
            
            headB=headB->next;
        
        
        }
        return NULL;
    }
};

//Second Approach TC0(n+m) , SC O(1)
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        ListNode *p=headA, * q=headB;
        while(p!=NULL && q!=NULL){
            if(p!=NULL && q!=NULL && p==q){
                return p;
            }
            p=p->next;
            q=q->next;
            
            if(p!=NULL && q!=NULL && p==q){
                return p;
            }

            if(p== NULL && q==NULL){
                return NULL;
              
            }
            if(p==NULL){
                swap(p,headB);
            }
            if(q==NULL){
                swap(q,headA);
            }
        }
        return NULL;
    }
};