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.

 

/**
 * 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 cur1 = headA;
        ListNode cur2 = headB;
        int n = 0;
        while (cur1.next != null) {
        	n++;
        	cur1 = cur1.next;
        }
        while (cur2.next != null) {
        	n--;
        	cur2 = cur2.next;
        }
        if (cur1 != cur2) {
        	return null;
        }
        cur1 = n > 0 ? headA : headB;
        cur2 = cur1 == headA ? headB : headA;
        n = Math.abs(n);
        while (n != 0) {
        	n--;
        	cur1 = cur1.next;
        }
        while (cur1 != cur2) {
        	cur1 = cur1.next;
        	cur2 = cur2.next;
        }
        return cur1;
    }
}