These are chat archives for camperbot/bonfire-no-repeats-please

22nd
Sep 2015
naxty
@naxty
Sep 22 2015 17:39
hint
CamperBot
@camperbot
Sep 22 2015 17:39

hint [1/7]

## :construction: After this are possible spoiler hints.

Make sure you've tried to hard to solve it yourself before proceeding. :construction:

type hint for next hint :pencil: [Contribute at the FCC Wiki]

naxty
@naxty
Sep 22 2015 17:39
hint
CamperBot
@camperbot
Sep 22 2015 17:39

hint [2/7]

# Problem Explanation:

  • This task requires us to look at each possible permutation of a string. This is best done using a recursion function. Being able to build a function which collects all permutations of a string is a common interview question, so there is no shortage of tutorials out there on how to do this, in many different code languages.
  • This task can still be daunting even after watching a tutorial. You will want to send each new use of the function 3 inputs: 1. a new string (or character array) that is being built, 2. a position in your new string that's going to be filled next, and 3. an idea of what characters (more specifically positions) from the original string have yet to be used. The pseudo code will look something like this:

    var str = ???;
    perm(current position in original string, what's been used in original string, current string build thus far){
    if(current string is finished) {
      print current string;
    }else{
      for(var i = 0; i < str.length; i++) {
        if(str[i] has not been used) {
          put str[i] into the current position;
          mark str[i] as used
          perm(current position in original string, what's been used in original string, current string build thus far)
          unmark str[i] as used because another branch in the tree for i + 1 will still likely use it;
        }
      }
    }
    }
    perm(0, nothing used yet, empty new string (or array the same size as str);
  • Another way to think about this problem is to start from an empty space. Introduce the first letter to the space. This space will now contain the first sub-permutation. Here's a diagram illustrating the idea:

diagram

// An approach to introduce a new character to a permutation
var ch = '?';
var source = ['?', '?', '?'];     // Current sub-permutation
var temp, dest = [];

for(var i = 0; i <= source.length; ++i) {
    temp = source.slice(0);    // Copy the array
    temp.splice(i, 0, ch);    // Insert the new character
    dest.push(temp);    // Store the new sub-permutation    
}

Finding each permutation could then be done non-recursively by including the above in a function taking a source array and returning a destination array. For each letter of the input string, pass that character, as well as the array returned from the previous call of the function.

A way to visualize this is by considering a tree that starts with the first character of your string: Permutation Tree

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naxty
@naxty
Sep 22 2015 17:40
hint
CamperBot
@camperbot
Sep 22 2015 17:40

hint [3/7]

Hint: 1

  • The easiest way is to use Heap's algorithm to recursively get a list of all the permutations.

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naxty
@naxty
Sep 22 2015 17:40
hint
CamperBot
@camperbot
Sep 22 2015 17:40

hint [4/7]

Hint: 2

  • Once you have the list then just create a regular expression to catch the repeating characters.

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naxty
@naxty
Sep 22 2015 17:45
hint
CamperBot
@camperbot
Sep 22 2015 17:45

hint [5/7]

Hint: 3

  • You will want to have the permutations as an array of joined strings instead of separated characters.

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naxty
@naxty
Sep 22 2015 17:45
hint
CamperBot
@camperbot
Sep 22 2015 17:45

hint [6/7]

Spoiler Alert!

687474703a2f2f7777772e796f75726472756d2e636f6d2f796f75726472756d2f696d616765732f323030372f31302f31302f7265645f7761726e696e675f7369676e5f322e676966.gif

Solution ahead!

type hint for next hint :pencil: [Contribute at the FCC Wiki]

naxty
@naxty
Sep 22 2015 17:45
hint
CamperBot
@camperbot
Sep 22 2015 17:45

hint [7/7]

Code Solution:

function permAlone(str) {

  // Create a regex to match repeated consecutive characters.
  var regex = /(.)\1+/g;

  // Split the string into an array of characters.
  var arr = str.split('');
  var permutations = [];
  var tmp;

  // FUnction to swap variables' content.
  function swap(index1, index2) {
    tmp = arr[index1];
    arr[index1] = arr[index2];
    arr[index2] = tmp;
  }

  //Generate arrays of permutations using the algorithm.
  function generate(int) {
    if (int === 1) {
      // Make sure to join the characters as we create  the permutation arrays
      permutations.push(arr.join(''));
    } else {
      for (var i = 0; i != int; ++i) {
        generate(int - 1);
        swap(int % 2 ? 0 : i, int - 1);
      }
    }
  }

  generate(arr.length);

  // Filter the array of repeated permutations.
  var filtered = permutations.filter(function(string) {
    return !string.match(regex);
  });

  //Return how many have no repetitions.
  return filtered.length;
}

Code Explanation:

  • Read comments in code

Credits:

If you found this page useful, you can give thanks by copying and pasting this on the main chat: thanks @Philosophist @Rafase282

NOTE: Please add your username only if you have added any relevant main contents to the wiki page. (Please don't remove any existing usernames.)

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Rafael J. Rodriguez
@Rafase282
Sep 22 2015 17:53
dude in one minute you went through everything including the answer?
remember to try writing your own code, asking people, hints, etc before looking at the code
naxty
@naxty
Sep 22 2015 17:56
tried it since yesterday
I am not a cheater
Rafael J. Rodriguez
@Rafase282
Sep 22 2015 17:57
not saying you are, just finished it yesterday and then got the notification and all the hints were displayed at the same time
your case aside cheating would only harm the cheater in this camp. So what gave you trouble?
naxty
@naxty
Sep 22 2015 17:58
I wrote to you in private
Rafael J. Rodriguez
@Rafase282
Sep 22 2015 17:58
I saw
Rafael J. Rodriguez
@Rafase282
Sep 22 2015 18:09
This message was deleted
Rafael J. Rodriguez
@Rafase282
Sep 22 2015 22:55
update
CamperBot
@camperbot
Sep 22 2015 22:55
updating wiki...
Updating 4278eb3..c977881 Fast-forward
Bonfire-Friendly-Date-Ranges.md | 95 +++++++++++++++++++++----- Bonfire-Seek-and-Destroy.md | 4 +- List-of-Free-Code-Camp-city-based-Campsites.md | 2 +- Select-Issues-for-Contributing-Using-Labels.md | 60 ++++++++-------- Wiki-Style-Guide.md | 10 +-- bonfire-mutations.md | 4 +- troll.md | 2 - 7 files changed, 119 insertions(+), 58 deletions(-) delete mode 100644 troll.md
done code: 0
:computer: