Pasted

public class Main {
    // Given a string of alphabets and a number k, write a function to print all of the combinations of length k of these alphabets.
    // The string does not contain duplicate alphabets.
    // EXPECTED OUTPUT: abd, abs, abe, ads, ade, ase, bds, bde, bse, dse.
    public static void main(String[] args) {
        char[] alphabet = { 'a', 'b', 'd', 's', 'e' };
        int k = 3; // length of output string.
 
        System.out.println("EXPECTED OUTPUT: abd, abs, abe, ads, ade, ase, bds, bde, bse, dse");
        System.out.print("ACTUAL OUTPUT: ");
        printAllCombinations(alphabet, k);
    }
 
    // Base function used to call the recursive version of itself with given alphabet and length, k.
    private static void printAllCombinations(char[] alphabet, int k) {
        // Initially set the prefix to "" and n to 0, while passing alphabet and length, k to printAllCombinations.
        printAllCombinations(alphabet, "", 0, k);
    }
 
    // Recursive method used to print all possible strings of length k, given a set of characters.
    // However, use n to keep track of your current location in the array alphabets.
    private static void printAllCombinations(char[] alphabet, String prefix, int n, int k) {
        // Base case: k is 0,
        // print prefix.
        if (k == 0) {
            // Only print ', ' if n is less than the length of the current prefix.
            if (n > prefix.length()) {
                System.out.print(", ");
            }
 
            System.out.print(prefix);
            return;
        }
 
        // One by one add all characters
        // from set and recursively
        // call for k equals to k - 1.
        // However, loop only from n to length of the alphabet.
        for (int i = n; i < alphabet.length; i++) {
            // Next character of input added.
            String newPrefix = prefix + alphabet[i];
 
            // k is decreased and n is increased, because
            // we have added a new character.
            printAllCombinations(alphabet, newPrefix, i + 1, k - 1);
        }
    }
}