Detect a Cycle in a Linked List

Detect a Cycle in a Linked List

Determine whether a linked list contains a cycle using Floyd's algorithm.

Input format

The first line contains N and POS — the 0-based index that the last node links back to (-1 for no cycle). The second line contains the N node values. The judge builds the cycle for you.

Output format

Print true if the list contains a cycle, otherwise false.

Constraints

• Values fit in a 64-bit signed integer
• Trailing whitespace and a trailing newline are ignored by the judge

Read from stdin, write to stdout. Sample cases below show the exact format.

4 1
3 2 0 -4

true

3 -1
1 2 3

false