74 lines
2.1 KiB
Python
74 lines
2.1 KiB
Python
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# Topic - Linkedlist
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# Language - Python
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# Problem - Detection and Removal of Cycle in Linkedlist.
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#
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# Idea - run 2 pointers at the start of the linkedlist
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# increment slow pointer by one and fast pointer by two nodes.
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# if slow pointer is equal to fast pointer - then cycle exist
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# to remove the cycle - we need to start slow pointer to start
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# and another fast pointer to same location it is pointing to
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# we will stop increamenting slow pointer when slow equals to
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# fast pointer and break the link from fast.next is None.
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class Node:
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def __init__(self, val):
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self.val = val
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self.next = None
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class Linkedlist:
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def __init__(self):
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self.head = None
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# pushAtStart is used to create linkedlist
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def pushAtStart(self, data):
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node = Node(data)
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node.next = self.head
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self.head = node
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def cycleDetectionAndRemoval(self):
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temp = self.head
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if temp is None or temp.next is None:
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return 'No Cycle Detected'
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slow_ptr = temp
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fast_ptr = temp
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while (slow_ptr and fast_ptr and fast_ptr.next):
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# moving slow pointer by one node and fast by two node.
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slow_ptr = slow_ptr.next
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fast_ptr = fast_ptr.next.next
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# if slow equals to fast, then we have encountered cycle
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if slow_ptr == fast_ptr:
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slow_ptr = temp
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while slow_ptr != fast_ptr:
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slow_ptr = slow_ptr.next
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fast_ptr = fast_ptr.next
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# removing cycle
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fast_ptr.next = None
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return 'Cycle Detected and Removed'
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return 'No Cycle Detected'
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if __name__ == '__main__':
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# creating linkedlist
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mylist = Linkedlist()
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# adding nodes
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mylist.pushAtStart(10)
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mylist.pushAtStart(20)
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mylist.pushAtStart(30)
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mylist.pushAtStart(40)
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mylist.pushAtStart(50)
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# creating cycle
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mylist.head.next.next.next.next.next = mylist.head.next.next
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# removing cycle
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print(mylist.cycleDetectionAndRemoval())
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# after removing cycle we don't have cycle
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print(mylist.cycleDetectionAndRemoval())
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