标签：style blog io color sp for on div 问题
Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
Follow up:
Can you solve it without using extra space?
首先指出：这个程序可以解决Linked List Cycle I的问题，同时之前Linked List Cycle I 的解法虽然可以AC但是破坏了链表结构，不是很合适
解题思路：让2个指针向前跑，一个一次跑一格，一个一次跑两格，如果有环，迟早相遇，在用一个指针从某个位置跑，通过关系式找到入口。
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ class Solution { public: ListNode *detectCycle(ListNode *head) { if(head==NULL || head->next == NULL)return NULL; ListNode *slow=head,*fast=head,*entry=head; while(fast->next && fast->next->next) { slow = slow->next; fast = fast->next->next; if(slow == fast) { while(slow != entry) { slow = slow->next; entry = entry->next; } return entry; } } return NULL; } };
标签：style blog io color sp for on div 问题
原文地址：http://www.cnblogs.com/55open/p/4158864.html
