Problem

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

Example

The following two linked lists:

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

begin to intersect at node c1.

Note

原理: A.length + Intersection + B.length = B.length + Intersection + A.length，也就是说，走了相同的三段长度之后，正好一起回到Intersection的起点。

Solution

public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        ListNode l1 = headA, l2 = headB;
        while (l1 != l2) {
            l1 = l1 == null ? headB: l1.next;
            l2 = l2 == null ? headA: l2.next;
        }
        return l1;
    }
}