列表中的项目数不按递增顺序排列

Question

def num_not_increasing(L)"""
    number of pairs in L that are not in increasing order. 
    switches([6, 1, 4]) returns 2, since (6, 1) and (6, 4) are out of order.
    """

我可以使用两个while循环和索引来轻松完成此操作，但是如何在python中递归地实现此目的呢？

编辑：我用while循环实现了什么：

def switches(L):
if len(L) < 2:
    return 0
else:
    i = 0
    j = 1
    count = 0
    while i  < len(L)-1:
        while j <len(L):
            if L[i] > L[j]:
                count+=1
            j+=1
        i+=1
    return count

Answer 1

你期待这个吗？

def COUNT(ind, prev, L):
    if(ind>=len(L)):
        return 0

    val = 0   

    val += COUNT(ind+1, prev, L)

    if(L[ind]<=L[prev]):
        val = val+1

    return val


def num_not_increasing(lst):
    val = 0
    for i in range(len(lst)):
        val += COUNT(i+1, i, lst)
    return val

L = [6,1,5,4,2]

print num_not_increasing(L)