Intersection of Two Linked Lists

1. Title

Intersection of Two Linked Lists

2. Http address

https://leetcode.com/problems/intersection-of-two-linked-lists/

3. The question

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.

4. My code (AC)

　　

    // Accepted
      public static ListNode getIntersectionNode(ListNode headA, ListNode headB) {
  
          if( headA == null || headB == null)
              return null;
          if( headA == headB)
              return headA;
          
          int lenA,lenB,distance;
          ListNode p,q;
          lenA = 0;
          p = headA;
          while( p != null)
          {
              lenA++;
              p = p.next;
          }
          
          lenB = 0;
          q = headB;
          while( q != null)
          {
              lenB++;
              q = q.next;
          }
          
          if( lenA >=lenB)
          {
              distance = lenA - lenB;
              p = headA;
              for(int i = 1; i <= distance; i++)
              {
                  p = p.next;
              }
              q = headB;
              while( p != null && q != null && p != q)
              {
                  p = p.next;
                  q = q.next;
              }
              return p;
          }else{
              distance = lenB - lenA;
              p = headB;
              for(int i = 1; i <= distance; i++)
              {
                  p = p.next;
              }
              q = headA;
              while( p != null && q != null && p != q)
              {
                  p = p.next;
                  q = q.next;
              }
              return p;
          }
          
      }