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 ListNode getIntersectionNode(ListNode headA, ListNode headB) { //boundary check if(headA == null || headB == null) { return null; } ListNode a = headA; ListNode b = headB; //这么写还是有点趣的,因为查完A list然后接着是 Blist,那么这样就可以不用考虑长度不等啦 while( a != b){ a = a == null? headB : a.next; b = b == null? headA : b.next; } return a; } public ListNode getIntersectionNode2(ListNode headA, ListNode headB) { if(headA==null || headB==null) { return null; } Set<ListNode> set = new HashSet<ListNode>(); ListNode a = headA; ListNode b = headB; while(a!=null) { set.add(a); a=a.next; } while(b!=null) { if(set.contains(b)) { return b; } b = b.next; } return null; }