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Linked List Cycle && Linked List Cycle II

2024-07-16 17:30:00   220人阅读

Linked List Cycle

Given a linked list, determine if it has a cycle in it.

Follow up: Can you solve it without using extra space?

 说明：两个指针不同步长。

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    bool hasCycle(ListNode *head) {        ListNode *p1, *p2;        p1 = p2 = head;        while(p2 && p2->next && p2->next->next) {            p2 = p2->next->next;            p1 = p1->next;            if(p1 == p2) return true;        }        return false;    }};

 

Linked List Cycle II

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?

 说明：在上题基础上，将一个指针放到链表头，步长都设为1，相遇节点。（可以计算）

class Solution {public:    ListNode *detectCycle(ListNode *head) {        ListNode *p1, *p2;        p1 = p2 = head;        while(p2 && p2->next && p2->next->next) {            p2 = p2->next->next;            p1 = p1->next;            if(p1 == p2) {                p1 = head;                while(p1 != p2) {                    p1 = p1->next;                    p2 = p2->next;                }                return p1;            }        }        return NULL;    }};

 

 


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