Create solution.cpp

Author: aishsingh

LinkedListCycle/solution.cpp

@@ -0,0 +1,38 @@
+/**
+ * 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) 
+    {
+        // Using Floyd's Cycle-Finding Algorithm
+        // SEE https://www.geeksforgeeks.org/floyds-cycle-finding-algorithm/
+        auto slowPtr = head;
+        auto fastPtr = head;
+
+        while (slowPtr != nullptr && 
+               fastPtr != nullptr && 
+               fastPtr->next != nullptr)    // this extra check needed only for the fast pointer as it will move 2 nodes at a time
+        {
+            slowPtr = slowPtr->next;
+            fastPtr = fastPtr->next->next;
+
+            if (slowPtr == fastPtr)
+            {
+                // slow pointer and fast pointer point to the same node
+                // this can only occur at this point if a cycle occured in the linked list
+                // cycle detected
+                return true;
+            }
+        }
+
+        // reached end of linked list
+        // cycle not detected
+        return false;
+    }
+};