Fletcher Checksum

Problem

Compute the Fletcher-16 checksum of a string: keep two running sums modulo 255, adding each character code to the first sum and then the first sum to the second, and return the second sum shifted left eight bits plus the first.

This detects both single-bit errors and many transpositions. The empty string gives 0.

Hint

The second sum accumulates the running value of the first, which makes order matter.

Test cases

case 1

in: [""]

expected: 0

case 2

in: ["a"]

expected: 24929

case 3

in: ["abc"]

expected: 19495

case 4

in: ["hello"]

expected: 11542

case 5

in: ["ABC"]

expected: 35782

Starter codePython

def fletcher_checksum(data):
    # Your code here
    pass

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