判断链表中是否有环

Author: DmrfCoder

LeetCode/Doc/判断链表中是否存在环.md

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+# linked-list-cycle(判断链表中是否存在环)
+
+<center>知识点：链表</center>
+
+
+## 题目描述
+
+Given a linked list, determine if it has a cycle in it.
+
+Follow up:
+Can you solve it without using extra space?
+
+给定一个链表，判断其中是否存在环。
+
+额外要求：
+尽量不要使用额外空间
+
+
+## 解题思路
+
+使用快慢指针即可。
+
+## 代码
+
+[这里](../src/ten/Solution.java)

LeetCode/src/ten/Solution.java

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+package ten;
+
+
+/**
+ * @author dmrfcoder
+ * @date 2019/4/10
+ */
+
+class ListNode {
+    int val;
+    ListNode next;
+
+    ListNode(int x) {
+        val = x;
+        next = null;
+    }
+}
+
+public class Solution {
+
+    public boolean hasCycle(ListNode head) {
+
+        if (head == null) {
+            return false;
+        }
+        ListNode fast, slow;
+        fast = slow = head;
+
+        while (fast.next != null && fast.next.next != null) {
+            fast = fast.next.next;
+            slow = slow.next;
+            if (fast == slow) {
+                return true;
+            }
+        }
+        return false;
+
+
+    }
+}

README.md

@@ -151,4 +151,5 @@
 - [binary-tree-preorder-traversal（先序遍历二叉树）](./LeetCode/Doc/先序遍历二叉树.md)
 - [reorder-list（链表重排序）](./LeetCode/Doc/链表重排序.md)
 - [linked-list-cycle-ii(找出链表中环的入口节点)](./LeetCode/Doc/找出链表中环的入口节点.md)
+- [linked-list-cycle(判断链表中是否存在环)](./LeetCode/Doc/判断链表中是否存在环.md)