**Explanation** Suppose `$1^{st}$`

group will be formed index `$1$`

to index `$2$`

, Then `$a_1 + a_2 = 7$`

. Now, `$k = 7\%10 = 7$`

. So, array `$a$`

will be `$\{3 + 7 , 4 - 7, 2 + 7, 4 - 7, 5 + 7\} = \{10, -3, 9, -3, 12\}$`

. The first group cost will be `$10 - 3 = 7$`

.

This is a companion discussion topic for the original entry at https://toph.co/p/operatorosim