Add Cycle Detection.py

Author: edaaydinea

Data Structures/02 - Linked Lists/Cycle Detection.py

@@ -0,0 +1,92 @@
+#!/bin/python3
+
+import os
+
+
+class SinglyLinkedListNode:
+    def __init__(self, node_data):
+        self.data = node_data
+        self.next = None
+
+
+class SinglyLinkedList:
+    def __init__(self):
+        self.head = None
+        self.tail = None
+
+    def insert_node(self, node_data):
+        node = SinglyLinkedListNode(node_data)
+
+        if not self.head:
+            self.head = node
+        else:
+            self.tail.next = node
+
+        self.tail = node
+
+
+def print_singly_linked_list(node, sep, fptr):
+    while node:
+        fptr.write(str(node.data))
+
+        node = node.next
+
+        if node:
+            fptr.write(sep)
+
+
+# Complete the has_cycle function below.
+
+#
+# For your reference:
+#
+# SinglyLinkedListNode:
+#     int data
+#     SinglyLinkedListNode next
+#
+#
+def has_cycle(head):
+    visited = set()
+    f = head
+    while f:
+        i = id(f)
+        if i in visited:
+            return 1
+        visited.add(i)
+        f = f.next
+    return 0
+
+
+if __name__ == '__main__':
+    fptr = open(os.environ['OUTPUT_PATH'], 'w')
+
+    tests = int(input())
+
+    for tests_itr in range(tests):
+        index = int(input())
+
+        llist_count = int(input())
+
+        llist = SinglyLinkedList()
+
+        for _ in range(llist_count):
+            llist_item = int(input())
+            llist.insert_node(llist_item)
+
+        extra = SinglyLinkedListNode(-1);
+        temp = llist.head;
+
+        for i in range(llist_count):
+            if i == index:
+                extra = temp
+
+            if i != llist_count - 1:
+                temp = temp.next
+
+        temp.next = extra
+
+        result = has_cycle(llist.head)
+
+        fptr.write(str(int(result)) + '\n')
+
+    fptr.close()