EasyNLPnlp-123

HMM Transition Count

Problem

Count tag transitions in a sequence, including boundary transitions. Insert a '<s>' start symbol before the first tag and a '</s>' end symbol after the last tag, then count adjacent pairs.

Return a dictionary keyed by 'from to'. An empty tag sequence yields an empty dictionary.

Hint

Track the previous symbol starting from '<s>' and finish with '</s>'.

Test cases

case 1

in: [["A","B","A"]]

expected: {"<s> A":1,"A B":1,"B A":1,"A </s>":1}

case 2

in: [[]]

expected: {}

case 3

in: [["X"]]

expected: {"<s> X":1,"X </s>":1}

case 4

in: [["A","A"]]

expected: {"<s> A":1,"A A":1,"A </s>":1}

Starter codePython

def hmm_transition_count(tags):
    # Your code here
    pass

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