20200711——第一百六十题 相交链表

/**
 * 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) {
        int counta = 0,countb =0;
        ListNode preA = headA,preB=headB;
        int length = 0;
        while(headA != null){
            counta++;
            headA = headA.next;
        }
        while(headB != null){
            countb++;
            headB = headB.next;
        }
        if(countb-counta>0){
            while(countb-counta-length!=0){
                length++;
                preB = preB.next;
            }
        }else{
            while(counta-countb-length >0){
                length++;
                preA=preA.next;
            }
        }
        while(preA != null && preB != null){
            if(preA == preB){
                return preA;
            }else{
                preA = preA.next;
                preB = preB.next;
            }
        }
        return null;
    }
}