/**
 * Definition for singly-linked list.
 */
#include <cstddef>
struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

// This solution is not great, being O(n^2)-ish time, although it is O(1) space, which is good.
// There is likely at least an O(n) in both solution...
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        while (headA) {
            ListNode* check = headB;
            while (check) {
                if (check == headA) {
                    return headA;
                }
                check = check->next;
            }
            headA = headA->next;
        }
        return nullptr;
    }
};