Linked List Cycle II
Given the head of a linked list, return the node where the cycle begins. If there is no cycle, return null.

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Linked List Cycle II
medium
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Given the head of a linked list, return the node where the cycle begins. If there is no cycle, return null.

Example 1:
Input: {"values":[3,2,0,-4],"cyclePos":1}
Output: [2,0,-4]
Constraints:

  • The number of nodes is in the range [0,104][0, 10^4].

  • −105≤Node.val≤105-10^5 \leq \text{Node.val} \leq 10^5

  • pos\text{pos} is −1-1 or a valid index in the linked list.

Input
arr ={"values":[3,2,0,-4],"cyclePos":1}

Find cycle start. List has cycle at index 1

Phase 1: Detect

Phase 2: Find Start

Linked List (cycle at index 1)
3

S

F

0

→
2

1

→
0

2

→
-4

3

↩ to [1]

Slow (S)
Fast (F)
Both Meet
Cycle Start
Variables
No variables to display
DepthFunction Call
Stack empty
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