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.

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

https://leetcode.com/problems/intersection-of-two-linked-lists/

package leetcode;
public class Solution
{
    public static ListNode getIntersectionNode(ListNode headA, ListNode headB)
    {
        int lenA=len(headA);
        int lenB=len(headB);
        while(lenA>lenB)
        {
            headA=headA.next;
            lenA--;
        }
        while(lenA<lenB)
        {
            headB=headB.next;
            lenB--;
        }
        while(headA!=headB)
        {
            headA=headA.next;
            headB=headB.next;
        }
        return headA;
    }
    public static int len(ListNode head)
    {
        int cout=0;
        while(head!=null)
        {
            head=head.next;
            cout++;
        }
        return cout;
    }
    public static void main(String args[])
    {
        ListNode a1=new ListNode(1);
        ListNode a2=new ListNode(2);
        ListNode a3=new ListNode(3);
        ListNode b1=new ListNode(4);
        ListNode b2=new ListNode(5);
        ListNode c1=new ListNode(6);
        ListNode c2=new ListNode(7);
        ListNode headA=new ListNode(0);
        ListNode headB=new ListNode(0);

        headA.next=a1;
        a1.next=a2;
        a2.next=a3;
//        a3.next=c1;
        c1.next=c2;
        headB.next=b1;
        b1.next=b2;
        b2.next=c1;
//        System.out.println(getIntersectionNode(headA,headB).val);
    }
}