Resolved: How to generate as much for loops in for loop as mentioned in function?

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Question:

I’m trying to generate all possible word combinations using a List<string>. For example, if I want to generate all possible word combinations of 2, the function would look like this:

public static List GenerateWordsOf2(List uniqueWords)
{
List unique2Words = new();
for (int i = 0; i < uniqueWords.Count; i++) { for (int j = 0; j < uniqueWords.Count; j++) { if (i != j) { unique2Words.Add(uniqueWords[i] + " " + uniqueWords[j]); } } } return unique2Words; } [/code]

This works as expected, but I when I want to generate, for example, unique words of 3, I would need to write a new function for that, making another loop inside it. Is there, maybe, a more effective way of doing this, like making a function that would take a number and generate that much of unique words list?

Answer:

You can do this iteratively, with a single for loop, as follows.
  • Start with a list containing only the “empty sentence”.
  • In each step, add each word to each previously constructed sentence.

Suppose uniqueWords is “a”, “b”, “c”.
  • At the start, you will have {“”}.
  • After the first step, you will have {“a”, “b”, “c”}
  • After the second step, you will have { “a+a”, “a+b”, “a+c”, “b+a”, “b+b”, “b+c”, “c+a”, “c+b”, “c+c”}
  • After the third step, you will get { “a+a+a”, “a+b+a”, … }

The only modification required is then to filter out duplicates. This leads to something like this (unoptimized) example:
using System; using System.Collections.Generic;

public class SentenceGenerator
{
public static List> ExpandSentences(List> partialSentences, List uniqueWords)
{
var newSentences = new List>();
foreach(var sentence in partialSentences)
{
foreach(var word in uniqueWords)
{
if(sentence.Contains(word))
{
continue;
}

// Make a copy of the old sentence
var newSentence = new List(sentence);

// Add a new word
newSentence.Add(word);

newSentences.Add(newSentence);
}
}

return newSentences;
}

public static void Main()
{
var uniqueWords = new List() {
“hello”,
“beautiful”,
“world”,
“full”,
“of”,
“people” };

var sentences = new List>() {
// Start with an empty sentence
new List()
};

for(int i = 1; i <= 3; i++) { sentences = ExpandSentences(sentences, uniqueWords); } System.Console.WriteLine("Generated " + sentences.Count + " sentences."); foreach(var sentence in sentences) { System.Console.WriteLine(string.Join(" ", sentence)); } } } [/code]

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