141. Linked List Cycle

Author: TBXark

141. Linked List Cycle.md

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+# 141. Linked List Cycle
+
+### 2017-03-23
+
+Given a linked list, determine if it has a cycle in it.
+
+Follow up:
+Can you solve it without using extra space?
+
+
+
+# Solution
+
+```c++
+/**
+ * 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) {
+			if(head == NULL) { return false; } 
+			ListNode *a = head;
+			ListNode *b = head;
+			while (b->next != NULL &&  b->next->next != NULL) {
+				a = a->next;
+				b = b->next->next;
+				if (a == b) { return true;}
+			}
+			return false;
+    }
+};
+```
+