CRDT PN-Counter Merge

Problem

Merge two PN-Counters from different replicas.

A PN-counter tracks positive and negative increments separately, and merging takes the element-wise maximum of both sides. a and b are dictionaries with "pos" and "neg" totals.

Return [merged_pos, merged_neg, merged_value].

Hint

Taking the maximum of each component makes the merge idempotent and commutative.

Test cases

case 1

in: [{"pos":3,"neg":1},{"pos":2,"neg":4}]

expected: [3,4,-1]

case 2

in: [{"pos":0,"neg":0},{"pos":5,"neg":2}]

expected: [5,2,3]

case 3

in: [{"pos":2,"neg":2},{"pos":2,"neg":2}]

expected: [2,2,0]

case 4

in: [{"pos":7,"neg":0},{"pos":1,"neg":1}]

expected: [7,1,6]

Starter codePython

def pn_counter_merge(a, b):
    # Your code here
    pass

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