I think k — sum1 < 0 for some cases .

Simply do this .

n = 4

1 2 3 4

set1 : 1 4

set2 : 2 3

n = 6

1 2 3 4 5 6

The ans will be no because odd number of pairs .

n = 8

1 2 3 4 5 6 7 8

set1 : 1 8 3 6

set2 : 2 7 4 5

Property of arithmetic progression .

Try taking n as long long. Your code is having integer overflow when you take n >= 1e5

Thanks both so much