【链表】BM6 判断链表中是否有环

BM6 判断链表中是否有环

快慢指针并求相遇点

力扣142

/**
 * 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) {
        ListNode* fast = head;
        ListNode* slow = head;
        while(fast != nullptr && fast->next != nullptr){
            fast = fast->next->next;
            slow = slow->next;
            if(fast == slow){
                ListNode* index1 = fast;
                ListNode* index2 = head;
                while(index1 != index2){
                    index1 = index1->next;
                    index2 = index2->next;
                }
                return index1;
            }
        }
        return nullptr;
    }
};

简单判断是否相遇

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
#include 
class Solution {
public:
    bool hasCycle(ListNode *head) {
        ListNode* fast = head;
        ListNode* slow = head;
        while(fast != nullptr && fast->next != nullptr){
            fast = fast->next->next;
            slow = slow->next;
            if(fast == slow){
                return true;
            }
        }
        return false;
    }
};