/src/spelling/corrector/DefaultSpellingCorrectorHelper.java

package spelling.corrector;



import java.util.ArrayList;

import java.util.Collection;

import java.util.Collections;

import java.util.List;

import java.util.TreeSet;





public class DefaultSpellingCorrectorHelper implements SpellingCorrectorHelper {

	

	public List<String> getDeletion(final String word) {

		List<String> deletions = new ArrayList<String>();

		for(int i=0;i<word.length();i++){

			String deletion = word.substring(0, i) + word.substring(i+1);

			deletions.add(deletion);

		}

		return Collections.unmodifiableList(deletions);

	}

	

	public List<String> getTransposition(final String word) {

		List<String> transpositions = new ArrayList<String>();

		for(int i=0;i<word.length()-1;i++){

			String transposition = word.substring(0, i) + word.charAt(i+1) + word.charAt(i)+ word.substring(i+2);

			transpositions.add(transposition);

		}

		return Collections.unmodifiableList(transpositions);

	}



	public List<String> getAlterations(final String word){

		List<String> alterations = new ArrayList<String>();

		for(int i=0;i<word.length();i++){

			for(Character current='a';current <='z';current++){

				String alteration = word.substring(0, i) + current +word.substring(i+1);

				alterations.add(alteration);

			}

		}

		return Collections.unmodifiableList(alterations);

	}



	public List<String> getInsertions(final String word){

		List<String> insertions = new ArrayList<String>();

		for(int i=0;i<word.length()+1;i++){

			for(Character current='a';current <='z';current++){

				String alteration = word.substring(0, i) + current +word.substring(i);

				insertions.add(alteration);

			}

		}

		return Collections.unmodifiableList(insertions);

	}



	public Collection<String> getFirstDegreeAlternatives(final String word){

		Collection<String> alternatives = new TreeSet<String>();

		alternatives.addAll(getDeletion(word));

		alternatives.addAll(getTransposition(word));

		alternatives.addAll(getAlterations(word));

		alternatives.addAll(getInsertions(word));

		return Collections.unmodifiableCollection(alternatives);

	}



	public Collection<String> getSecondDegreeAlternatives(final Collection<String> words){

		Collection<String> alternatives = new TreeSet<String>();

		for(String alternative : words){

			alternatives.addAll(getFirstDegreeAlternatives(alternative));

		}

		return Collections.unmodifiableCollection(alternatives);

	}

}