https://leetcode.com/problems/intersection-of-two-linked-lists/description/
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.
//time:o(n) space:o(1)
1 public ListNode getIntersectionNode(ListNode headA, ListNode headB) { 2 if (headA == null || headB == null) { 3 return null; 4 } 5 int lengthA = getLength(headA); 6 int lengthB = getLength(headB); 7 ListNode currA = headA; 8 ListNode currB = headB; 9 if (lengthA > lengthB) { 10 while (lengthA != lengthB) { 11 currA = currA.next; 12 lengthA--; 13 } 14 } else { 15 while (lengthB != lengthA){ 16 currB = currB.next ; 17 lengthB--; 18 } 19 } 20 //now they are the same length 21 while (currA!=currB ){ 22 currA = currA.next ; 23 currB = currB.next ; 24 } 25 //out of while, means currA == currB, including both == null 26 return currA ; 27 } 28 29 private int getLength(ListNode head) { 30 int length = 1; 31 while (head != null) { 32 head = head.next; 33 length++; 34 } 35 return length; 36 }
