Python 队列可写

a=int(input())
k=list(map(int,input().split()))
t=[0]*(max(k)+1)
st=[0]*1000
top=0
tail=0
for i in range(a):
    t[k[i]]+=1
for i in range(len(t)):
    while t[i]!=0:
        if tail!=top and i>st[top]:
            top+=1
        st[tail]=i
        tail+=1
        t[i]-=1     
print(tail-top)