Problem description

I am attempting to define a function that counts the maximum number of items in an array that are already sorted based on any given array. For example,
[1, 2, 3] should return 3 as it is fully sorted, [3, 2, 1] should return 0, and 0, 2, 1 should return 2. Can anyone help me? Thanks!

>Solution :

We can create a one-liner function (no builtin exists)

Code

def count_ordered(lst): 
    return sum(x==y for x, y in zip(lst, sorted(lst)))

Tests

count_ordered([0, 1, 2]) # returns 3
count_ordered([0, 2, 1]) # returns 1
count_ordered([3, 2, 1]) # returns 1 

Explanation

The function counts the number of elements that match before and after sorting.