dsa · easy

Linked List Cycle II (start)

GreyOrangeLinked ListTwo PointersFoundation

head is node values, pos is the index the tail links back to (-1 = no cycle). Reconstruct the list and return the **index where the cycle starts**, or -1.

Arguments

• head — the linked list, given as a Python list of node values
• pos — 0-based index the tail links back to, or -1 if there is no cycle

**Example:** head=[3,2,0,-4], pos=1 → 1.

Constraints

0 <= len(head) <= 4*10^4 Hidden tests include near-max size for this bound; a slower-than-intended solution TLEs.

Examples

Example 1

Input:
[3,2,0,-4]
1

Expected:
1

Example 2

Input:
[1,2]
-1

Expected:
-1

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