leetcode 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
• 从后对齐，只需比较后面的元素，有没有相同的
• 没有中间有一个相同的，后面又不同的情况

• /**
   * 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) {
          ListNode result = null;
  		ListNode tempa=headA;
  		ListNode tempb=headB;
  		if (headA == null || headB == null) {
  			return null;
  		}
  		int a = 1, b = 1;
  		while (headA.next != null) {
  			a++;
  			headA = headA.next;
  		}
  		while (headB.next != null) {
  			b++;
  			headB = headB.next;
  		}
  		int temp = 0;
  		if (a >= b) {
  			temp = a - b;
  			while (temp != 0) {
  				tempa = tempa.next;
  				temp--;
  			}
  		} else {
  			temp = b - a;
  			while (temp != 0) {
  				tempb = tempb.next;
  				temp--;
  			}
  		}
  		while (tempa!= null) {
  			if (tempa == tempb) {
  				result = tempa;
  				break;
  			} else {
  				tempa = tempa.next;
  				tempb = tempb.next;
  			}
  		}
  		return result;
      }
  }