标签：
Question：
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.
1、题型分类：
2、思路：
3、时间复杂度：O(n)
4、代码：
空间复杂度O(n)
public class Solution { public ListNode getIntersectionNode(ListNode headA, ListNode headB) { if(headA==null || headB==null) return null; Set<ListNode> set=new HashSet<ListNode>(); while(headA!=null) { if(set.contains(headA)) return headA; else set.add(headA); headA=headA.next; } while(headB!=null) { if(set.contains(headB)) return headB; else set.add(headB); headB=headB.next; } return null; } }
5、优化：
先计算两个链表的长度，然后分别从相同长度的节点开始遍历，遇到相同的元素返回。
public class Solution { public ListNode getIntersectionNode(ListNode headA, ListNode headB) { int lenA = getLen(headA); int lenB = getLen(headB); ListNode shortHead = headA; ListNode longHead = headB; if (lenA > lenB) { shortHead = headB; longHead = headA; } int i = 0; while (i < Math.abs(lenB - lenA)) { i++; longHead = longHead.next; } while (shortHead != longHead) { shortHead = shortHead.next; longHead = longHead.next; if (shortHead == null) { return null; } } return shortHead; } private int getLen(ListNode head) { int len = 0; while (head != null) { len++; head = head.next; } return len; } }
6、扩展：
[LeetCode] Intersection of Two Linked Lists
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原文地址：http://www.cnblogs.com/maydow/p/4644150.html
