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.

Given a date string, determine which day of the year it represents (e.g., January 1st is day 1). Calculate the day number accounting for leap years.

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).