https://programmers.co.kr/learn/courses/30/lessons/42862
def solution(n, lost, reserve):
answer = 0
stu=[1]*n
for i in lost:
stu[i-1]-=1
for i in reserve:
stu[i-1]+=1
for i in range(n):
if stu[i]==0:
if i!=0 and stu[i-1]>1:
stu[i-1]-=1
stu[i]+=1
elif i!=n-1 and stu[i+1]>1:
stu[i+1]-=1
stu[i]+=1
answer=n-stu.count(0)
return answer