CF352B Jeff and Periods

One day Jeff got hold of an integer sequence $ a_{1} $ , $ a_{2} $ , $ ... $ , $ a_{n} $ of length $ n $ . The boy immediately decided to analyze the sequence. For that, he needs to find all values of $ x $ , for which these conditions hold: - $ x $ occurs in sequence $ a $ . - Consider all positions of numbers $ x $ in the sequence $ a $ (such $ i $ , that $ a_{i}=x $ ). These numbers, sorted in the increasing order, must form an arithmetic progression. Help Jeff, find all $ x $ that meet the problem conditions.

The first line contains integer $ n $ $ (1

In the first line print integer $ t $ — the number of valid $ x $ . On each of the next $ t $ lines print two integers $ x $ and $ p_{x} $ , where $ x $ is current suitable value, $ p_{x} $ is the common difference between numbers in the progression (if $ x $ occurs exactly once in the sequence, $ p_{x} $ must equal 0). Print the pairs in the order of increasing $ x $ .

In the first test $ 2 $ occurs exactly once in the sequence, ergo $ p_{2}=0 $ .