Java Program to print all permutations of a given string
A permutation also called an “arrangement number” or “order,” is a rearrangement of the elements of an ordered list S into a one-to-one correspondence with S itself. A string of length n has n! permutation.
Source: Mathword(http://mathworld.wolfram.com/Permutation.html)
Below are the permutations of string ABC.
ABC ACB BAC BCA CBA CAB
Here is a solution that is used as a basis in backtracking.
Java
// Java program to print all // permutations of a given string. public class Permutation { public static void main(String[] args) { String str = "ABC" ; int n = str.length(); Permutation permutation = new Permutation(); permutation.permute(str, 0 , n- 1 ); } /* Permutation function @param str string to calculate permutation for @param l starting index @param r end index */ private void permute(String str, int l, int r) { if (l == r) System.out.println(str); else { for ( int i = l; i <= r; i++) { str = swap(str,l,i); permute(str, l+ 1 , r); str = swap(str,l,i); } } } /* Swap Characters at position @param a string value @param i position 1 @param j position 2 @return swapped string */ public String swap(String a, int i, int j) { char temp; char [] charArray = a.toCharArray(); temp = charArray[i] ; charArray[i] = charArray[j]; charArray[j] = temp; return String.valueOf(charArray); } } // This code is contributed by Mihir Joshi |
Output:
ABC ACB BAC BCA CBA CAB
Algorithm Paradigm: Backtracking
Time Complexity: O(n*n!) Note that there are n! permutations and it requires O(n) time to print a permutation.
Auxiliary Space: O(r – l)
Note: The above solution prints duplicate permutations if there are repeating characters in the input string. Please see the below link for a solution that prints only distinct permutations even if there are duplicates in input.
Print all distinct permutations of a given string with duplicates.
Permutations of a given string using STL
Another approach:
Java
import java.util.*; // Java program to implement // the above approach class GFG{ static void permute(String s, String answer) { if (s.length() == 0 ) { System.out.print(answer + " " ); return ; } for ( int i = 0 ;i < s.length(); i++) { char ch = s.charAt(i); String left_substr = s.substring( 0 , i); String right_substr = s.substring(i + 1 ); String rest = left_substr + right_substr; permute(rest, answer + ch); } } // Driver code public static void main(String args[]) { Scanner scan = new Scanner(System.in); String s; String answer= "" ; System.out.print( "Enter the string : " ); s = scan.next(); System.out.print( "\nAll possible strings are : " ); permute(s, answer); } } // This code is contributed by adityapande88 |
Output:
Enter the string : abc All possible strings are : abc acb bac bca cab cba
Time Complexity: O(n*n!) The time complexity is the same as the above approach, i.e. there are n! permutations and it requires O(n) time to print a permutation.
Auxiliary Space: O(|s|)