Longest Arithmetic Stretch

Difficulty: 1200 3000 ms 128 MB

implementation

Find the longest CONTIGUOUS stretch that forms an arithmetic progression (constant difference).

Input: the first line has N; the second line has N integers.

Output: the maximum AP stretch length (any 1 or 2 elements always qualify).

Constraints:

• 1 ≤ N ≤ 10⁵
• |a_i| ≤ 10⁹

Sample Tests

7
3 5 7 9 2 4 6

4

2
1 9

2

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