python 牛客真题 数列还原

考察全排列？

nk=list(input().split())
n=int(nk[0])
k=int(nk[1])
num=[int(c) for c in list(input().split())]
m=[0]*(n+1)
index=[]
for i in range(n):
    if num[i]==0: index.append(i)
    else: m[num[i]]=1
a=[]
for i in range(1,n+1):
    if m[i]==0: a.append(i)
def cal(num):
    count=0
    for i in range(n-1):
        for j in range(i+1,n):
            if num[i]<num[j]: count+=1 
    return count
def permute(a):
        res=[]
        def dfs(nums,tmp):
            if len(nums) == len(tmp):
                res.append(tmp[:])
            for m in nums:
                if m in tmp:
                    continue 
                tmp.append(m)
                dfs(nums,tmp)
                tmp.remove(m)
        dfs(a,[])
        return res
res=permute(a)
cnt=0
for list1 in res:
    count=0
    for i in range(len(a)):
        num[index[i]]=list1[i]
    if k==cal(num): cnt+=1
print(cnt)