Check Alternating Highs and Lows Around a Circular Array

An array is connected end to end to form a circle. Determine whether its values strictly alternate between a high point and a low point around the entire circle.

Implement is_alternating_circle(values: int[]) -> bool. Every element must be strictly greater than both of its neighbors or strictly less than both of its neighbors. The first and last elements are neighbors.

Constraints & Assumptions

• There are between 2 and 200,000 elements, each between -1,000,000,000 and 1,000,000,000.
• Equal neighboring values are not allowed in a valid alternating circle.
• For length two, both neighbor positions of an element refer to the other element. Two distinct values therefore form a valid alternating circle.
• Strict comparisons and the length-two convention are explicit practice choices for the reported high/low pattern.
• Return one Boolean; no rotation or rearrangement of the input is allowed.

Examples

• [1, 4, 2, 5] returns true. Each low value has two higher neighbors and each high value has two lower neighbors, including across the last-to-first boundary.
• [1, 4, 2] returns false. The value 2 is lower than 4 but higher than 1, so it is neither a high nor a low point.