You're given an array of numbers and a target value 'k'. You can apply specific operations to array elements to maximize the array's sum; determine the minimum number of operations needed to make the sum greater than or equal to k.

Find two numbers in an array that form a 'strong pair' (where one number is no more than twice the other). Maximize the XOR result of all possible strong pairs, and return that maximum value.

Rearrange the digits of a given number to form the largest possible number. You can only swap digits with the same parity (even or odd).