Intersection of Two Linked Lists

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists: 

A:          a1 → a2
                   ↘
                     c1 → c2 → c3
                   ↗            
B:     b1 → b2 → b3

begin to intersect at node c1.

Notes:

• If the two linked lists have no intersection at all, return null.
• The linked lists must retain their original structure after the function returns. 
• You may assume there are no cycles anywhere in the entire linked structure.
• Your code should preferably run in O(n) time and use only O(1) memory.

Runtime: 72ms

/**
 * 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) {
        if(!headA || !headB) return NULL;
        
        if(getLength(headA) > getLength(headB)){
            int len = getLength(headA);
            while(len > getLength(headB)){
                headA = headA->next;
                len--;
            }
        }
        else{
            int len = getLength(headB);
            while(len > getLength(headA)){
                headB = headB->next;
                len--;
            }
        }
        
        while(headA){
            if(headA == headB)
                return headA;
            headA = headA->next;
            headB = headB->next;
        }
        return NULL;
    }
    
    int getLength(ListNode* head){
        int result = 0;
        
        while(head){
            head = head->next;
            result++;
        }
        return result;
    }
};