Nooks Software Engineer Interview Experience — Phone Screen on Merging Labeler Consensus, Rejected

It should be the same question as before.

Use a machine to label phone call recordings. Each recording is 100 seconds long. There are N labelers and only 3 labels [human, machine, silence]. The result is determined by consensus (> N / 2), and the result is also 100 seconds long. If there is any stretch of time with no consensus, you need to raise an error.

input:

labelers =
[
[('0.0', '10.5', 'human'), ('10.5', '20.0', 'machine'), ('20.0', '100.0', 'silence')],
[('0.0', '9.0', 'human'), ('9.0', '20.0', 'silence'), ('20.0', '100.0', 'human')],
[('0.0', '20.0', 'silence'), ('20.0', '100.0', 'human')]
]

output:

labels = [('0.0', '9.0', 'human'), ('9.0', '20.0', 'silence'), ('20.0', '100.0', 'human')]

Good luck!

Update (2026-10-30 13:02 +08:00): I failed. Leaving a working solution here.

from collections import Counter

def consensus_segments(labelers):
    """Pass 1: repeatedly take the earliest head end, vote on that stretch, then advance the heads.
    Works directly on the input: each labeler's list is consumed from the front,
    so the lists are empty when this returns.
    """
    pieces = []
    while True:
        heads = [labeler[0] for labeler in labelers if labeler]
        if not heads:
            break
        start = min(h[0] for h in heads)
        end = min(h[1] for h in heads)  # earliest end among the heads
        votes = [h[2] for h in heads]
        label, count = Counter(votes).most_common(1)[0]
        winner = label if count > len(labelers) / 2 else None  # needs more than half of the labelers
        pieces.append((start, end, winner))
        for labeler in labelers:
            if labeler:
                s, e, lab = labeler[0]
                if e == end:
                    labeler.pop(0)                # head fully used up, drop it
                else:
                    labeler[0] = (end, e, lab)    # head is longer, shrink it from the left
    return pieces

def merge_adjacent(pieces):
    """Pass 2: join touching segments that have the same label."""
    if not pieces: return []
    merged = []
    cur_start, cur_end, cur_label = pieces[0]  # start with the first piece
    for start, end, label in pieces[1:]:       # go through the remaining pieces
        if start == cur_end and label == cur_label:
            cur_end = end                      # touching and same label: extend current segment
        else:
            merged.append((cur_start, cur_end, cur_label))  # close the current segment
            cur_start, cur_end, cur_label = start, end, label
    merged.append((cur_start, cur_end, cur_label))  # don't forget the last one
    return merged

def merge_labelers(labelers):
    return merge_adjacent(consensus_segments(labelers))

if __name__ == "__main__":
    labelers = [
        [(0.0, 10.5, 'human'), (10.5, 20.0, 'machine'), (20.0, 100.0, 'silence')],
        [(0.0, 9.0, 'human'), (9.0, 20.0, 'silence'), (20.0, 100.0, 'human')],
        [(0.0, 20.0, 'silence'), (20.0, 100.0, 'human')],
    ]
    pieces = consensus_segments(labelers)
    print(pieces)
    labels = merge_adjacent(pieces)
    print(labels)
    assert labels == [(0.0, 9.0, 'human'), (9.0, 20.0, 'silence'), (20.0, 100.0, 'human')]

    # no label has more than half of the votes -> no winner
    no_majority = [
        [(0.0, 10.0, 'human')],
        [(0.0, 10.0, 'machine')],
        [(0.0, 10.0, 'silence')],
    ]
    result = merge_labelers(no_majority)
    print(result)
    assert result == [(0.0, 10.0, None)]