Implementation: Reddit ranking algorithm in Notes

25 Jan 2015

Reddit ranking algorithm to sort hot stories is quite robust and works out of the box. Moreover, Reddit is open sourced and code is free available.

We picked out the same ranking algorithm and applied it on HackerEarth Notes. The results were exactly what it intended to do and served our purpose.

Below is the code in Python, which you can use in similar scenarios. We made a small modification to the hot() function arguments as we don't support downvote in Notes.

Reddit ranking algorithm.

from datetime import datetime, timedelta
from math import log

epoch = datetime(1970, 1, 1)

def epoch_seconds(date):
    """Returns the number of seconds from the epoch to date."""
    td = date - epoch
    return td.days * 86400 + td.seconds + (float(td.microseconds) / 1000000)

def score(ups, downs=0):
    return ups - downs

def hot(ups, date, downs=0):
    """The hot formula."""
    s = score(ups, downs)
    order = log(max(abs(s), 1), 10)
    sign = 1 if s > 0 else -1 if s < 0 else 0
    seconds = epoch_seconds(date) - 1134028003
    return round(order + sign * seconds / 45000, 7)

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Posted by Vivek Prakash.

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