Digital Content

Cory Doctorow describes this problem pretty bluntly as: “If you can’t open it, you don’t own it.”

What You’re Buying When You Buy Digital Content

How Do I Get Rid of the DRM on My Ebooks and Video?

Just as a quick primer here, we should note what exactly it is you’re purchasing when you buy digital content, and why this problem exists in the first place. When you purchase digital content, you’re typically just buying a license to use it. You do not “own” the books or media you purchase in traditional terms. For example, here’sAmazon’s Terms of Use (bolding ours):P

Upon your download of Kindle Content and payment of any applicable fees (including applicable taxes), the Content Provider grants you a non-exclusive right to view, use, and display such Kindle Content an unlimited number of times, solely on the Kindle or a Reading Application or as otherwise permitted as part of the Service, solely on the number of Kindles or Supported Devices specified in the Kindle Store, and solely for your personal, non-commercial use. Kindle Content is licensed, not sold, to you by the Content Provider.P

Most Terms of Use at other digital stores follow Amazon here, and they all also have something similar to this little caveat:P

In addition, you may not bypass, modify, defeat, or circumvent security features that protect the Kindle Content.P

So, just so you know: removing DRM from ebooks and videos is typically against the Terms of Use. Most services like Amazon or Barnes and Noble allow you to store your books or video purchases in the cloud so you can download them again later. But they’re always restricted to their apps.

Epubor Ultimate Converter helps you one-click to decrypt and convert eBooks purchased from Kindle, Nook, Sony, Kobo and Google online eBook stores in batch. This fantastic and award-winning software is a “must-have” tool for all eBook lovers. It’s the most easy-to-use eBook format conversion software ever, and it’s 100% safe with no adware, spyware, or viruses.

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ePUBee also have PDF DRM Removal and Kindle DRM Removalhelp you remove DRM from PDF/AZW for free.

Design and Analysis of Algorithms

Course Features

Course Description

This is an intermediate algorithms course with an emphasis on teaching techniques for the design and analysis of efficient algorithms, emphasizing methods of application. Topics include divide-and-conquer, randomization, dynamic programming, greedy algorithms, incremental improvement, complexity, and cryptography.

Note on Previous Versions:

The Spring 2015 version of 6.046 contains substantially different content than the Spring 2005 version. The 2005 version was an introductory algorithms course assuming minimal previous experience, while the 2015 version is an intermediate course requiring a semester of introductory material found in 6.006.

Other OCW Versions

OCW has published multiple versions of this subject. Question_OVT logo

dancing links

In computer science, dancing links is the technique suggested by Donald Knuth to efficiently implement his Algorithm X.[1] Algorithm X is a recursive, nondeterministic, depth-first, backtracking algorithm that finds all solutions to the exact cover problem. Some of the better-known exact cover problems include tiling, the n queens problem, and Sudoku.

The name dancing links stems from the way the algorithm works, as iterations of the algorithm cause the links to “dance” with partner links so as to resemble an “exquisitely choreographed dance.” Knuth credits Hiroshi Hitotsumatsu and Kōhei Noshita with having invented the idea in 1979,[2] but it is his paper which has popularized it.

“Algorithm X” is the name Donald Knuth used in his paper “Dancing Links” to refer to “the most obvious trial-and-error approach” for finding all solutions to the exact coverproblem.[1] Technically, Algorithm X is a recursive, nondeterministic, depth-first, backtracking algorithm. While Algorithm X is generally useful as a succinct explanation of how theexact cover problem may be solved, Knuth’s intent in presenting it was merely to demonstrate the utility of the dancing links technique via an efficient implementation he called DLX.[1]

The exact cover problem is represented in Algorithm X using a matrix A consisting of 0s and 1s. The goal is to select a subset of the rows so that the digit 1 appears in each column exactly once.

Algorithm X functions as follows:

  1. If the matrix A has no columns, the current partial solution is a valid solution; terminate successfully.
  2. Otherwise choose a column c (deterministically).
  3. Choose a row r such that Ar, c = 1 (nondeterministically).
  4. Include row r in the partial solution.
  5. For each column j such that Ar, j = 1,
    for each row i such that Ai, j = 1,

    delete row i from matrix A.
    delete column j from matrix A.
  6. Repeat this algorithm recursively on the reduced matrix A.

The nondeterministic choice of r means that the algorithm essentially clones itself into independent subalgorithms; each subalgorithm inherits the current matrix A, but reduces it with respect to a different row r. If column c is entirely zero, there are no subalgorithms and the process terminates unsuccessfully.

The subalgorithms form a search tree in a natural way, with the original problem at the root and with level k containing each subalgorithm that corresponds to k chosen rows. Backtracking is the process of traversing the tree in preorder, depth first.

Any systematic rule for choosing column c in this procedure will find all solutions, but some rules work much better than others. To reduce the number of iterations, Knuthsuggests that the column choosing algorithm select a column with the lowest number of 1s in it.