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Linked List Cycle Detection

Given a list and a pos (0-indexed position where the tail connects to form a cycle), return True if there is a cycle, False otherwise. pos = -1 means no cycle.

Example:

Input:

3,2,0,-4
1

Output:

True

Reasoning:

The input list is created as $3 \rightarrow 2 \rightarrow 0 \rightarrow -4$ , with each number representing a node's value.
The input pos = 1 indicates that the tail of the list connects to the node at index 1, forming a cycle: $3 \rightarrow 2 \rightarrow 0 \rightarrow -4 \rightarrow 2$ .
We can detect this cycle using the two-pointer technique, where one pointer moves twice as fast as the other, and if there is a cycle, these two pointers will eventually meet.
Since the pointers meet at the node with value 2, we conclude that a cycle exists in the list.
The final output is therefore True.

Constraints:

0 <= number of nodes <= 10^4
-10^5 <= Node.val <= 10^5
pos is -1 or a valid index

Editor

Python 3.13.1

Test Results

0/0

Run code to see test results.