Forward-Fill vs Back-Fill Difference

Problem

Count the positions where forward filling and backward filling disagree. Forward fill carries the last known value downward (leading gaps seed from the first known value); backward fill carries the next known value upward (trailing gaps seed from the last known value).

Return the number of positions where the two filled series differ, or 0 if the series has no known values.

Hint

A gap disagrees when its two ends have different values.

Test cases

case 1

in: [[1,null,3]]

expected: 1

case 2

in: [[null,2,null,4]]

expected: 1

case 3

in: [[1,2,3]]

expected: 0

case 4

in: [[null,null]]

expected: 0

Starter codePython

def forward_back_fill_difference(series):
    # Your code here
    pass

4 test cases · run your code against them in the editor