CF1513A Array and Peaks

A sequence of $ n $ integers is called a permutation if it contains all integers from $ 1 $ to $ n $ exactly once. Given two integers $ n $ and $ k $ , construct a permutation $ a $ of numbers from $ 1 $ to $ n $ which has exactly $ k $ peaks. An index $ i $ of an array $ a $ of size $ n $ is said to be a peak if $ 1 < i < n $ and $ a_i \gt a_{i-1} $ and $ a_i \gt a_{i+1} $ . If such permutation is not possible, then print $ -1 $ .

N/A

N/A

In the second test case of the example, we have array $ a = [2,4,1,5,3] $ . Here, indices $ i=2 $ and $ i=4 $ are the peaks of the array. This is because $ (a_{2} \gt a_{1} $ , $ a_{2} \gt a_{3}) $ and $ (a_{4} \gt a_{3} $ , $ a_{4} \gt a_{5}) $ .