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.

Solution:

1 /** 2  * Definition for singly-linked list. 3  * public class ListNode { 4  *     int val; 5  *     ListNode next; 6  *     ListNode(int x) { 7  *         val = x; 8  *         next = null; 9  *     }10  * }11  */12 public class Solution {13     public ListNode getIntersectionNode(ListNode headA, ListNode headB) {14         if (headA==null || headB==null) return null;15 16         ListNode s1 = headA;17         ListNode s2 = headB;18         int len1 = 1;19         while (s1.next!=null){20             len1++;21             s1 = s1.next;22         }23         int len2 = 1;24         while (s2.next!=null){25             len2++;26             s2=s2.next;27         }28         s1 = headA;29         s2 = headB;30         if (len1>len2){31             while (len1>len2){32                 s1 = s1.next;33                 len1--;34             }35         } else if (len1