Why assigning one pointer to another changes original pointer in cpp?

Question

Suppose headA points to [1, 3, 5, 7, 9, 11] and headB points to [2, 4,9, 11]. I want to find the common intersecting elementproblem statement

I am not understanding why a_pointer and b_pointer is returning a null list in the end.

I followed this tutorial

Algorithm followed:(as below)

#include<bits/stdc++.h>


    struct ListNode {
        int val;
        ListNode *next;
        ListNode() : val(0), next(nullptr) {}
        ListNode(int x) : val(x), next(nullptr) {}
        ListNode(int x, ListNode *head) { val = x;  next = head; }
    };


    class Solution {

    public:

        void print(ListNode *head)
        {
            while(head != nullptr)
            {
                printf("%d ->", head->val );
                head = head->next;
            }
            printf("\n");
        }

        
                ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {


                    print(headA);
                    print(headB);

                    ListNode *a_pointer, *b_pointer;
                    a_pointer = headA;
                    b_pointer = headB;

                    while(a_pointer != b_pointer)
                    {
                        

                        if(a_pointer == nullptr)
                        {
                            a_pointer = headB;
                        }
                        else
                        {
                            a_pointer = a_pointer->next;
                        }

                        if(b_pointer == nullptr)
                        {
                            b_pointer = headA;
                        }
                        else
                        {
                            b_pointer = b_pointer->next;
                        }

                    }

                    print(a_pointer);
                    print(b_pointer);
                    return a_pointer;   

                }


            };



    int main()
    {
        Solution s;
        ListNode *node1 = new ListNode(1);
        node1->next = new ListNode(3);
        node1->next->next = new ListNode(5);
        node1->next->next->next = new ListNode(7);
        node1->next->next->next->next = new ListNode(9);
        node1->next->next->next->next->next = new ListNode(11);

        ListNode *node2 = new ListNode(2);
        node2->next = new ListNode(4);
        node2->next->next = new ListNode(9);
        node2->next->next->next = new ListNode(11);

        
        ListNode *ret = s.getIntersectionNode(node1,node2);
        
    }

Answer 1

I am not understanding why the assignment a_pointer = headB is changing the original headB pointer.

It is reasonable to not understand why original headB pointer would be changed, because the original headB pointer is not being changed.