How to maximize rewards with exactly k tasks

You are assigning n independent tasks to two interns.

• Each task must be done by exactly one intern.
• If intern 1 does task i , you earn reward1[i] points.
• If intern 2 does task i , you earn reward2[i] points.
• Intern 1 must be assigned exactly k tasks ; intern 2 gets the remaining n - k tasks.
• Tasks can be assigned in any order (no contiguity requirement).

Goal: Return the maximum total points achievable.

Input

• reward1 : integer array of length n
• reward2 : integer array of length n
• k : integer ( 0 ≤ k ≤ n )

Output

• An integer: the maximum possible total reward.

Notes / Expected Complexity

Design an algorithm that works efficiently for large n (e.g., up to 10^5).