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.

 

Java Solution

 1 public class ListNode {
 2  　　int val;
 3  　　ListNode next;
 4  　　ListNode(int x) {
 5  　　    val = x;
 6  　　    next = null;
 7  　　}
 8  }
 9  
10 
11  public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
12       ListNode p1 = headA, p2 = headB;
13       int len1 = 0, len2 = 0;
14       while (p1 != null) {
15           p1 = p1.next;
16           len1++;
17       }
18       while (p2 != null) {
19           p2 = p2.next;
20          len2++;
21      }
22      p1 = headA;
23      p2 = headB;
24      if (len1 > len2) {
25          for (int i = 0;i < len1 - len2; i++) {
26              p1 = p1.next;
27          }
28      } else {
29          for (int i = 0;i < len2 - len1; i++) {
30              p2 = p2.next;
31          }
32      }
33      while (p1 != p2) {
34          p1 = p1.next;
35          p2 = p2.next;
36      }
37      return p1;
38  }

 

 

posted @ 2016-04-20 22:05  Dennis_XD  阅读(158)  评论(0)    收藏  举报