160. Intersection of Two Linked Lists java solutions

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.

Credits:
Special thanks to @stellari for adding this problem and creating all test cases.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        if(headA == null || headB == null) return null;
        ListNode ca = headA, cb = headB;
        int cnta = 0, cntb = 0;
        while(ca != null){
            cnta++;
            ca = ca.next;
        }
        while(cb != null){
            cntb++;
            cb = cb.next;
        }
        int sub = Math.abs(cnta - cntb);
        if(cnta > cntb){
            while(sub > 0){
                headA = headA.next;
                sub--;
            }
        }else{
            while(sub > 0){
                headB = headB.next;
                sub--;
            } 
        }
        while(headA != headB){
            headA = headA.next;
            headB = headB.next;
        }
        return headA;
    }
}