23.相交链表

方法一：哈希集合

/*** 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) {Set<ListNode> visited = new HashSet<>();ListNode tmp = headA;while(tmp!=null){visited.add(tmp);tmp = tmp.next;}tmp = headB;while(tmp != null){if(visited.contains(tmp)){return tmp;}tmp = tmp.next;}return null;}
}

方法二：双指针

/*** 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) {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;}
}