/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
// 最容易想到的是hashmap
// 双指针法 
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        if(headA == null || headB == null) return null;
        ListNode pA = headA; ListNode pB = headB;
        while(pA != pB){
            pA = pA == null? headB:pA.next;
            pB = pB == null? headA:pB.next;
        }
        return pA;
    }
}