united-coders.com - python

facebook Hacker Cup 2012 Qualification - solution for billboards

Christian Harms — Wed, 25 Jan 2012 18:50:17 +0000

The second problem from this year facebook hackercup sound like the classic knapsack problem. But the solution is much easier (words are in fixed sort order). Feel free to find a smarter algorithm or comment my python solution.

problem description

We are starting preparations for Hacker Cup 2013 really early. Our first step is to prepare billboards to advertise the contest. We have text for hundreds of billboards, but we need your help to design them.Read more

Q*Bert chrismas tree puzzle

Christian Harms — Mon, 19 Dec 2011 12:28:05 +0000

This is a short coding puzzle with q*bert (who is q*bert?) and an chrismas tree.

the qbert question

The task: Our 2011 q*bert can only jump down. He start from the top and has to find the path to the bottom of the chrismas tree with collecting the most points available (while jumping left-or-right down). Find the way with the highest sum.

Input:

chrismasTree = [[75],
              [95,64],
            [17,47,82],
          [18,35,87,10],
        [20, 4,82,47,65],
      [19, 1,23,75, 3,34] ]
print qbertRun(chrismasTree)

The sum is 465 - try to solve it with a little program. The brute force method will be possible with this small tree.Read more

Use compressed data directly - from ZIP files or gzip http response

Christian Harms — Mon, 17 Oct 2011 13:02:44 +0000

Did you use compressing while using resources from your scripts and projects? Many data files are compressed to save disc space and compressed requests over the network saves bandwith.

This article gives some hints to use the “battery included” power of python for the handling of compressed files or use HTTP with gzip compression:

reading log files as GZIP or uncompressed
using files directly from ZIP- or RAR compression archive
use gzip compressing while fetching web sites

Read more

basic rules for code readability and the if statement

Christian Harms — Mon, 01 Aug 2011 16:55:23 +0000

Some reader knows my preference for programming languages like python or javascript. One reason is the readability (yes, this is possible with many languages except brainfuck or whitespace). Once we write some lines of code, but other developer has to read the lines of code several times while code reviews, debugging or refactoring.

Code should be readable like your normal language. I will start with a funny condition.

if ( !notOk != false ) {
  userObj.ask();
}

This is only confusing and you will never formulate this expression in a natural language. With several steps this term can be simply resolved:

( !notOk != false )
( !notOk == true )
( !notOk)
now you should rethink the variable name: isOk = !notOk

And the result is more readable:Read more

comparing language performance and memory usage

Christian Harms — Fri, 10 Jun 2011 08:46:35 +0000

With the small coding contest some weeks ago we got many comments and it’s worth to make a conclusion for the solutions in different languages. What language is easier to write, has better memory usage or better performance?

To clarify the question:

Remove duplicate lines from a file

We have a text file with 13 Million entries, all numbers in the range from 1.000.000 to 100.000.000. Each line has only one number. The file is unordered and we have about 1% duplicate entries. Remove the duplicates.

Be efficient with the memory usage and / or find a performant solution. The script should be started with the filename and linenumber and print the result to stdout.Read more

Google Code Jam - Minimum Scalar Product

Nico Heid — Sun, 10 Apr 2011 12:52:54 +0000

With the Google Code Jam 2011 less than four weeks away, it is time for some finger exercises.

Let's start with the Minimum Scalar Product, which should only take you a few minutes.

Here's the Java version, which will only work for the small input set. I'll explain later.

public static int getMinimumScalarProduct2(int[] x, int[] y) {
 
        Arrays.sort(x);
        Arrays.sort(y);
        int sum=0;
 
        for (int i = 0; i < x.length; i++) {
            sum += x[i] * y[x.length -1 -i];
        }
        return sum;
    }

What we do is sort both arrays, then multiply them. One starting from the beginning, the other from the end. So our biggest numbers are multiplied with the smallest. The math is on Google's solution page, we're just looking at coding here.Read more

10 one-line solutions for project euler

Christian Harms — Tue, 28 Dec 2010 13:00:16 +0000

What are one-line solutions?

Solving an problem from project euler can be a challenge or coding fun. The result of every problem is only one number, calculated by an algorithm. Some algorithms can be written as one expression. You get an one-liner if you can embed it in a function with only one line of code.

What is Project Euler?

Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.

After solving some project euler problems with python I got some one-line solutions with nice usage of list comprehensions and functional programming. These code examples are not clean code but a challenge to find more one-line solutions. This article include my first 10 solutions for project euler as one-line python function. Dont use it to cheating the project - it should be a motivation to find smart coding solutions and participate to project euler. Read more

Google code jam solution for alien language

Christian Harms — Mon, 30 Aug 2010 09:58:16 +0000

Problem

In the 2009 qualification round there was a simple problem with a nice background story:

After years of study, scientists at Google Labs have discovered an alien language transmitted from a faraway planet. The alien language is very unique in that every word consists of exactly L lowercase letters. Also, there are exactly D words in this language.

Once the dictionary of all the words in the alien language was built, the next breakthrough was to discover that the aliens have been transmitting messages to Earth for the past decade. Unfortunately, these signals are weakened due to the distance between our two planets and some of the words may be misinterpreted. In order to help them decipher these messages, the scientists have asked you to devise an algorithm that will determine the number of possible interpretations for a given pattern.Read more

The rotate google contest in 15 lines

Christian Harms — Thu, 19 Aug 2010 11:35:38 +0000

The rotate example nico last week reported was funny to solve: No rotating needed! Read the complete problem description in nicos article or in the google code contest page. Here my complete python solution with file handling and solution printing.

import sys
from re import search
 
fp = file(sys.argv[1])
for case in range(1, 1+int(fp.next())):
    n, k = [int(x) for x in fp.next().split()]
    lines = [fp.next() for x in range(n)]
    
    #right-gravitation and joining to one line (delim is a line)
    s = "#".join(map(lambda x:"%%%ds"%n%(x.strip().replace(".","")), lines))
    result = 0
 
    #find one of the 4 variants: horiz, verti, slash, backslash for Blue
    reB = "(B.{%%d}){%d}B" % (k-1)

Read more

Image resizing tips general and for python

Christian Harms — Sun, 21 Mar 2010 23:15:27 +0000

Generating thumbnails from a collection of pictures is an easy task and there are many tools for the job. But I didn't find a tool who can clip out a centered box of my pictures to get quadratic thumbs of my originals. Because I am a developer and I dont want to try out many tools: I will hack a short python script (with help of the PIL) myself.

simple solution

The following python script can be find on many webpages. It will take all command line arguments as image filenames and convert it to 200x200 thumbnails with the default extension "_thumb.jpg" (build from the original filename):

import Image, os, sys
 
for filename in sys.argv[1:]:
    img = Image.open(filename).resize( (200,200) )
    out = file(os.path.splitext(filename)[0]+"_thumb.jpg", "w")
    try:
        img.save(out, "JPEG")
    finally:
        out.close()

Read more