| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

New TLS Implementation; Maths for Physicists; How I Am 8; 1000 Word Philosophy; Cyberpunk Reading List; Detailed Discussion of Message Dispatch in ParserCombinator Library for Julia; FizzBuzz in Julia w Dependent Types; kokko - Design Shop in Osaka; Summary of Greece, Currently; LLVM and GPUs; See Also; Schoolgirl Groyps (Maths); Japanese Lit; Another Example - Modular Arithmetic; Music from United; Read Agatha Christie for the Plot; A Constructive Look at TempleOS; Music Thread w Many Recommendations; Fixed Version; A Useful Julia Macro To Define Equality And Hash; k3b cdrom access, OpenSuse 13.1; Week 2; From outside, the UK looks less than stellar; Huge Fonts in VirtualBox; Keen - Complex Emergencies; The Fallen of World War II; Some Spanish Fiction; Calling C From Fortran 95; Bjork DJ Set; Z3 Example With Python; Week 1; Useful Guide To Starting With IJulia; UK Election + Media; Review: Reinventing Organizations; Inline Assembly With Julia / LLVM; Against the definition of types; Dumb Crypto Paper; The Search For Quasi-Periodicity...; Is There An Alternative To Processing?; CARDIAC (CARDboard Illustrative Aid to Computation); The Bolivian Case Against Chile At The Hague; Clear, Cogent Economic Arguments For Immigration; A Program To Say If I Am Working; Decent Cards For Ill People; New Photo; Luksic And Barrick Gold; President Bachelet's Speech; Baltimore Primer; libxml2 Parsing Stream; configure.ac Recipe For Library Path; The Davalos Affair For Idiots; Not The Onion: Google Fireside Chat w Kissinger; Bicycle Wheels, Inertia, and Energy; Another Tax Fraud; Google's Borg; A Verion That Redirects To Local HTTP Server; Spanish Accents For Idiots; Aluminium Cans; Advice on Spray Painting; Female View of Online Chat From a Male; UX Reading List; S4 Subgroups - Geometric Interpretation; Fucking Email; The SQM Affair For Idiots; Using Kolmogorov Complexity; Oblique Strategies in bash; Curses Tools; Markov Chain Monte Carlo Without all the Bullshit; Email Para Matias Godoy Mercado; The Penta Affair For Idiots; Example Code To Create numpy Array in C; Good Article on Bias in Graphic Design (NYTimes); Do You Backup github?; Data Mining Books; SimpleDateFormat should be synchronized; British Words; Chinese Govt Intercepts External Web To DDOS github; Numbering Permutations; Teenage Engineering - Low Price Synths; GCHQ Can Do Whatever It Wants; Dublinesque; A Cryptographic SAT Solver; Security Challenges; Word Lists for Crosswords; 3D Printing and Speaker Design; Searchable Snowden Archive; XCode Backdoored; Derived Apps Have Malware (CIA); Rowhammer - Hacking Software Via Hardware (DRAM) Bugs; Immutable SQL Database (Kinda); Tor GPS Tracker; That PyCon Dongle Mess...; ASCII Fluid Dynamics; Brandalism; Table of Shifter, Cassette and Derailleur Compatability; Lenovo Demonstrates How Bad HTTPS Is; Telegraph Owned by HSBC; Smaptop - Sunrise (Music); Equation Group (NSA); UK Torture in NI; And - A Natural Extension To Regexps; This Is The Future Of Religion

© 2006-2015 Andrew Cooke (site) / post authors (content).

Hyperpublic's Challenge

From: andrew cooke <andrew@...>

Date: Fri, 25 Feb 2011 09:07:26 -0300

Since other people have posted solutions and linked to them from HN I thought
I may as well post mine.


First question is based on summing "influences" defined in a matrix.  Given
the form of the input it's simplest to construct a set of delayed functions,
one per input line.  These can then be called, and call each other to
calculate the sum.  Memoization would help, but isn't needed for such a small
problem.

#!/usr/bin/python3

# see http://hyperpublic.com/challenge/question1

from itertools import count
from sys import argv

# read test file from command line
filename = argv[1] if len(argv) > 1 else 'challenge2input.txt'

# build tree of functions that terminate in users with no influence
# scorers array allows reference to functions not yet defined
def make_scorer(line):
    def scorer(scorers):
        return sum(1 + scorers[user](scorers)
                   for (user, char) in zip(count(), line)
                   if char == 'X')
    return scorer

scorers = [make_scorer(line) for line in open(filename)]
scores = [scorer(scorers) for scorer in scorers]
scores.sort(reverse=True)
print(scores)
print('result', ''.join(str(score) for score in scores[0:3]))


Second question involves plitting the score for a user into groups of points,
so that the minimum number of groups are used.  Apparently this is a ell known
problem called "coin change", which makes sense.  I didn't know that, but did
see that a dynamic solution is going to work (if you start with N points then
the best solution is going to be with group i if the solution with N-P(i) is
smallest; repeat...).

I am pretty sure you can write this directly as a recursive expression with
memoization, but it's easier to just build the anser from the bottom:

#!/usr/bin/python3

# see http://hyperpublic.com/challenge/question2

from operator import mul
from functools import reduce

scores = [2349, 2102, 2001, 1747]
points = [98, 42, 23, 17, 3, 2]

big = 1+max(*scores)
best = [None] * big # either None or (min number, history)

# simple dynamic solution, building from bottom up
for n in range(big):
    for p in points:
        if n == p:
            best[n] = (1, [p])
            break
        elif n > p and best[n-p]:
            (m, h) = best[n-p]
            if not best[n] or best[n][0] > m+1:
                best[n] = (m+1, h+[p])

assert best[20] == (2, [3,17])
assert best[34] == (2, [17,17]) # not greedy

for score in scores:
    (n, history) = best[score]
    print(score, n, history)

print('result', reduce(mul, map(lambda score: best[score][0], scores)))


Andrew

Comment on this post