How to Find All Permutations of a String in Java – Example

In mathematics, the notion of permutation is used with several slightly different meanings, all related to the act of permuting (rearranging) objects or values. Informally, a permutation of a set of objects is an arrangement of those objects into a particular order. For example, there are six permutations of the set {1,2,3}, namely (1,2,3), (1,3,2), (2,1,3), (2,3,1), (3,1,2), and (3,2,1).

Here is a quick simple Algorithm which computes all Permutations of a String Object in Java.

• First take out the first char from String and permute the remaining chars
• If String = “123”
• First char = 1 and remaining chars permutations are 23 and 32.
• Now we can insert first char in the available positions in the permutations.
• 23 -> 123, 213, 231
• 22 -> 132, 312, 321

package com.crunchify.tutorials;

import java.util.HashSet;
import java.util.Set;

/**
 * @author Crunchify.com
 * 
 */

public class CrunchifyMarmutationExample {

	public static void main(String[] args) {
		String s = "ABC";
		String s1 = "EBAY";
		String s2 = "Yahoo";
		System.out.println("\nString " + s + ":\nPermutations: " + crunchifyPermutation(s));
		System.out.println("\nString " + s1 + ":\nPermutations: " + crunchifyPermutation(s1));
		System.out.println("\nString " + s2 + ":\nPermutations: " + crunchifyPermutation(s2));
	}

	public static Set<String> crunchifyPermutation(String str) {
		Set<String> crunchifyResult = new HashSet<String>();
		if (str == null) {
			return null;
		} else if (str.length() == 0) {
			crunchifyResult.add("");
			return crunchifyResult;
		}

		char firstChar = str.charAt(0);
		String rem = str.substring(1);
		Set<String> words = crunchifyPermutation(rem);
		for (String newString : words) {
			for (int i = 0; i <= newString.length(); i++) {
				crunchifyResult.add(crunchifyCharAdd(newString, firstChar, i));
			}
		}
		return crunchifyResult;
	}

	public static String crunchifyCharAdd(String str, char c, int j) {
		String first = str.substring(0, j);
		String last = str.substring(j);
		return first + c + last;
	}

}

String ABC:
Permutations: [ACB, ABC, BCA, CBA, CAB, BAC]

String EBAY:
Permutations: [YBEA, EYAB, EBYA, YABE, YAEB, BYEA, EYBA, BAEY, AYBE, ABYE, AEYB, AYEB, ABEY, BEYA, YBAE, EBAY, EAYB, BYAE, AEBY, YEAB, YEBA, BEAY, EABY, BAYE]

String Yahoo:
Permutations: [hYaoo, ooahY, oYoha, hooaY, aoYho, Yooha, ahooY, oaoYh, Yhoao, haYoo, hoaoY, ohoYa, haoYo, haooY, oaYoh, ooYah, oohaY, aYhoo, aoYoh, hooYa, aYooh, Yaoho, ohaoY, Yhooa, Yohao, Yohoa, hoYao, oahoY, aooYh, hoYoa, oYaoh, ohaYo, ohYoa, hYoao, Yahoo, oYoah, Yoaoh, aohYo, hoaYo, ahYoo, ahoYo, ooYha, ohYao, aoohY, oYaho, oohYa, aYoho, Yhaoo, ooaYh, oYhoa, Yoaho, Yooah, oahYo, hYooa, oaohY, ohoaY, Yaooh, oYhao, aohoY, oaYho]

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