CF1400D Zigzags

You are given an array $ a_1, a_2 \dots a_n $ . Calculate the number of tuples $ (i, j, k, l) $ such that: - $ 1 \le i < j < k < l \le n $ ; - $ a_i = a_k $ and $ a_j = a_l $ ;

N/A

N/A

In the first test case, for any four indices $ i < j < k < l $ are valid, so the answer is the number of tuples. In the second test case, there are $ 2 $ valid tuples: - $ (1, 2, 4, 6) $ : $ a_1 = a_4 $ and $ a_2 = a_6 $ ; - $ (1, 3, 4, 6) $ : $ a_1 = a_4 $ and $ a_3 = a_6 $ .