https://programmers.co.kr/learn/courses/30/lessons/12987
def solution(A, B):
A.sort()
B.sort()
answer = 0
i, j = 0, 0
while i < len(A) and j < len(B):
if A[i] < B[j]:
answer += 1
i += 1
j += 1
else:
j += 1
return answer