solve problem Linked List Cycle

Author: P-ppc

README.md

@@ -139,6 +139,7 @@ All solutions will be accepted!
 |290|[Word Pattern](https://leetcode-cn.com/problems/word-pattern/description/)|[java/py/js](./algorithms/WordPattern)|Easy|
 |205|[Isomorphic Strings](https://leetcode-cn.com/problems/isomorphic-strings/description/)|[java/py/js](./algorithms/IsomorphicStrings)|Easy|
 |125|[Valid Palindrome](https://leetcode-cn.com/problems/valid-palindrome/description/)|[java/py/js](./algorithms/ValidPalindrome)|Easy|
+|141|[Linked List Cycle](https://leetcode-cn.com/problems/linked-list-cycle/description/)|[java/py/js](./algorithms/LinkedListCycle)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/LinkedListCycle/README.md

@@ -0,0 +1,2 @@
+# Linked List Cycle
+This problem is easy to solve by double pointer

algorithms/LinkedListCycle/Solution.java

@@ -0,0 +1,31 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+    public boolean hasCycle(ListNode head) {
+        ListNode p1 = head,
+                 p2 = head;
+        
+        while (p1 != null && p2 != null) {
+            p1 = p1.next;
+            p2 = p2.next;
+            if (p2 != null && p2.next != null) {
+                if (p1 == p2.next) {
+                    return true;
+                } else {
+                    p2 = p2.next;
+                }
+            }
+        }
+        
+        return false;
+    }
+}

algorithms/LinkedListCycle/solution.js

@@ -0,0 +1,30 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+
+/**
+ * @param {ListNode} head
+ * @return {boolean}
+ */
+var hasCycle = function(head) {
+    let p1 = head,
+        p2 = head
+    
+    while (p1 && p2) {
+        p1 = p1.next
+        p2 = p2.next
+        if (p2 && p2.next) {
+            if (p1 === p2.next) {
+                return true
+            } else {
+                p2 = p2.next
+            }
+        }
+    }
+    
+    return false
+};

algorithms/LinkedListCycle/solution.py

@@ -0,0 +1,25 @@
+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution(object):
+    def hasCycle(self, head):
+        """
+        :type head: ListNode
+        :rtype: bool
+        """
+        p1 = head
+        p2 = head
+        
+        while p1 and p2:
+            p1 = p1.next
+            p2 = p2.next
+            if p2 and p2.next:
+                if p1 == p2.next:
+                    return True
+                else:
+                    p2 = p2.next
+        
+        return False