diff --git a/docs/Leetcode_Solutions/JavaScript/0141._Linked_List_Cycle.md b/docs/Leetcode_Solutions/JavaScript/0141._Linked_List_Cycle.md new file mode 100644 index 0000000000000000000000000000000000000000..91124fcd7c23660399eb6d1eecc85644700d8cef --- /dev/null +++ b/docs/Leetcode_Solutions/JavaScript/0141._Linked_List_Cycle.md @@ -0,0 +1,109 @@ +# 001. Two Sum + +**难度: Easy** + +## 刷题内容 + +> 原题连接 + +* https://leetcode.com/problems/linked-list-cycle/ + +> 内容描述 + +``` +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. +``` + +![img](https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist.png) + +**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. +``` + +![img](https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist_test2.png) + +**Example 3:** + +``` +Input: head = [1], pos = -1 +Output: false +Explanation: There is no cycle in the linked list. +``` + +![img](https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist_test3.png) + + + +**Follow up:** + +Can you solve it using *O(1)* (i.e. constant) memory? + + + +## 解题方案 + +> 思路 1 +******- 时间复杂度: O(N)******- 空间复杂度: O(N)****** + +使用`快慢指针`的思路进行解题。就像两个运动员在同一个环形赛道上赛跑,如果一个运动员跑的快,一个跑得慢,最后两个运动员一定会相遇。 + +下面代码中的`fast`每次会走两步,而`slow`每次会走一步,如果`fast`没有`next`节点,自然没有环;如果`fast`等于`slow`说明二者相遇,最终为表明存在环。 + + + +#### 执行结果 + +执行用时 :**92 ms**, 在所有 JavaScript 提交中击败了94.16%的用户 + +内存消耗 :**36.6 MB**, 在所有 JavaScript 提交中击败了51.93% + + + +代码: + +```javascript +/** + * Definition for singly-linked list. + * function ListNode(val) { + * this.val = val; + * this.next = null; + * } + */ + +/** + * @param {ListNode} head + * @return {boolean} + */ +var hasCycle = function(head) { + if (head === null || head.next === null) { + return false + } + + let slow = head + let fast = head.next + + while (slow !== fast) { + if (fast === null || fast.next === null) { + return false + } + slow = slow.next + fast = fast.next.next + } + return true +}; +``` +