160. Intersection of Two Linked Lists(java)

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.

  public class Solution {    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {        if(headA==null||headB==null) return null;        ListNode p = headA;        ListNode q = headB;        int La=0;        int Lb=0;        while(p.next!=null){            La++;            p=p.next;        }        while(q.next!=null){            Lb++;            q=q.next;        }                int diff = 0;        p=headA;        q=headB;        if(La>Lb){            diff = La-Lb;            int i=0;            while(i<diff){                p=p.next;                i++;}        }else{            diff=Lb-La;            int i=0;            while(i<diff){                q=q.next;                i++;            }}        while(p!=null&&q!=null){            if(p==q){                 return p;            }else {                p=p.next;                q=q.next;} }         return null;}}