feat : liked-list-cycle

Author: ekgns33

linked-list-cycle/ekgns33.java

@@ -0,0 +1,35 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+
+/*
+* input : singly linked list and head node
+* output : return true if list has cycle
+*
+* solution : tortoise and hare algorithm
+*   with two pointer (slow and fast)
+* tc : O(n)
+* sc : O(1)
+*
+* */
+public class Solution {
+  public boolean hasCycle(ListNode head) {
+    if(head == null) return false;
+    ListNode slow = head;
+    ListNode fast = head;
+    while(fast.next != null && fast.next.next != null) {
+      slow = slow.next;
+      fast = fast.next.next;
+      if(fast == slow) return true;
+    }
+    return false;
+  }
+}