Go Premium for a chance to win a PS4. Enter to Win

x
Solved

# string combinatorics, generate  nCr strings from n strings

Posted on 2011-09-22
Medium Priority
588 Views
I have a set of n strings. I would like to extract all combinations of strings from these n strings . (all nCr combinations). How can  I do this programmatically.
For example :
Input : a,b,c,d,e
Output :
a,b,c,d
a,b,c,e
a,b,d,e
a,c,d,e
b,c,d,e
a,b,c
a,c,d
a,d,e
......and so on till

a,b
b,a
and so on till
a
b
c
d
e
0
Question by:TrialUser
• 5
• 2

LVL 37

Expert Comment

ID: 36580129
The best way is to make a function that finds all string combinations of length N and use that recursively.
Then you just call it for each length.

``````
ArrayList FindAllStrings(string input)
{
ArrayList strings;

for(int i = 0; i<=input.Length(); i++)
}

{
if(N == 0)
else
{
for(int i = 0; i + N < input.Length(); i++)
}
``````
0

LVL 37

Accepted Solution

TommySzalapski earned 2000 total points
ID: 36580206
Tested and fixed
``````        private ArrayList FindAllStrings(string input)
{
ArrayList strings = new ArrayList();

for (int i = 0; i <= input.Length; i++)

return strings;
}

private void AddStrings(ArrayList strings, string input, int N, string leading = "")
{
if (N == 0)
else
{
for (int i = 0; i + N <= input.Length; i++)
}
}
``````
0

LVL 37

Expert Comment

ID: 36580224
If you want the commas, change line 18 to
AddStrings(strings, input.Substring(i + 1), N - 1, leading + (leading.Length > 0 ? ",":"") + input[ i]);
0

LVL 86

Expert Comment

ID: 36581969
Use the libaray here written by Adrian Akison:
http://www.codeproject.com/KB/recipes/Combinatorics.aspx

Simple Demo: Idle-Mind-502573.flv

Click on Project --> Add Reference --> Browse --> Facet.Combinatorics.dll

Then you want to use the Variations class like this:
``````using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
listBox1.DataSource = Variations(textBox1.Text);
}

private List<string> Variations(string input)
{
List<string> values = new List<string>();
for (int i=0; i < input.Length; i++)
{
}

List<string> results = new List<string>();
for (int i = input.Length; i >= 1; i--)
{
Facet.Combinatorics.Variations<string> vars = new Facet.Combinatorics.Variations<string>(values.AsReadOnly(), i);
foreach (IList<string> set in vars)
{
}
}
return results;
}
}
}
``````

Here's the output:
``````a,b,c,d
a,b,d,c
a,c,b,d
a,d,b,c
a,c,d,b
a,d,c,b
b,a,c,d
b,a,d,c
c,a,b,d
d,a,b,c
c,a,d,b
d,a,c,b
b,c,a,d
b,d,a,c
c,b,a,d
d,b,a,c
c,d,a,b
d,c,a,b
b,c,d,a
b,d,c,a
c,b,d,a
d,b,c,a
c,d,b,a
d,c,b,a
a,b,c
a,b,d
a,c,b
a,d,b
a,c,d
a,d,c
b,a,c
b,a,d
c,a,b
d,a,b
c,a,d
d,a,c
b,c,a
b,d,a
c,b,a
d,b,a
c,d,a
d,c,a
b,c,d
b,d,c
c,b,d
d,b,c
c,d,b
d,c,b
a,b
a,c
a,d
b,a
c,a
d,a
b,c
b,d
c,b
d,b
c,d
d,c
a
b
c
d
``````

0

LVL 37

Expert Comment

ID: 36582051
Idle_Mind, that does all the possible permutations of all the possible combinations. It's also using another library and even then, the code looks just about as long as mine.

TrialUser, I assume your inclusion of both a,b and b,a was accidental and you just wanted the combinations. To do all permutations in mine you would just change
input.Substring(i + 1)
to
input.Substring(0,i) + input.Substring(i + 1)
0

LVL 37

Expert Comment

ID: 36582067
You do need to make sure to have
using System.Collections
at the top to use the ArrayList or you could modify the code to use whatever collection type you prefer.
0

LVL 86

Expert Comment

ID: 36582072
The library can also do Permuations and Combinations as well...it's pretty flexible.
0

LVL 13

Expert Comment

ID: 36904484
Just last week I was solving a Permutation problem on ProjectEuler.net and came across this website. http://www.bearcave.com/random_hacks/permute.html

In particular, I found this graphic interesting, http://www.bearcave.com/random_hacks/permute_diagram.jpg

Merely implementing that, with an otter loop that iterates through removing letters solves it.
0

## Featured Post

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

One of Google's most recent algorithm changes affecting local searches is entitled "The Pigeon Update." This update has dramatically enhanced search inquires for the keyword "Yelp." Google searches with the word "Yelp" included will now yield Yelp a…
Exception Handling is in the core of any application that is able to dignify its name. In this article, I'll guide you through the process of writing a DRY (Don't Repeat Yourself) Exception Handling mechanism, using Aspect Oriented Programming.
I've attached the XLSM Excel spreadsheet I used in the video and also text files containing the macros used below. https://filedb.experts-exchange.com/incoming/2017/03_w12/1151775/Permutations.txt https://filedb.experts-exchange.com/incoming/201…
Exchange organizations may use the Journaling Agent of the Transport Service to archive messages going through Exchange. However, if the Transport Service is integrated with some email content management application (such as an anti-spam), the admin…
###### Suggested Courses
Course of the Month6 days, 19 hours left to enroll