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  • 141. Linked List Cycle(判断l链表是否有环)(leetcode)

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

    To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in the linked list where tail connects to. If pos is -1, then there is no cycle in the linked list.

    Example 1:

    Input: head = [3,2,0,-4], pos = 1
    Output: true
    Explanation: There is a cycle in the linked list, where tail connects to the second node.
    

    Example 2:

    Input: head = [1,2], pos = 0
    Output: true
    Explanation: There is a cycle in the linked list, where tail connects to the first node.
    

    Example 3:

    Input: head = [1], pos = -1
    Output: false
    Explanation: There is no cycle in the linked list.
    

    Follow up:

    Can you solve it using O(1) (i.e. constant) memory?

    方法一:双指针

    1、一个指针移动一步,一个指针移动两步,如果两个指针相遇则有环。

    2、做任何题,第一个应该想的是鲁棒性

    算法复杂度:o(n)           运行时间:0ms        占用空间:38.6ms

    方法二:哈希表

    1、什么时候想到用哈希表?如果要查找一个元素是否在一个集合中。常常想到哈希表。如果用键值对用hashmap,否则用hashset。

    算法复杂度:o(n)           运行时间:5ms        占用空间:37.5ms

    苟有恒,何必三更眠五更起;最无益,莫过一日暴十日寒。
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  • 原文地址:https://www.cnblogs.com/shaer/p/10419736.html
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