Problem statement

https://binarysearch.com/problems/K-Compare/

Solution

Just sort b and then use binary search. Or find number of elements, which are < sorted(b)[-k]

Complexity

It is O(m log m + n) for time and O(m + n) for space.

Code

class Solution:
    def solve(self, a, b, k):
        if not k: return len(a)
        target = sorted(b)[-k]
        return sum(x < target for x in a)