Recursion-8

Q1. Given the number of diZits n in a number, print all n-diZit numbers whose diZits are strictly increasinZ
from left to riZht.
i/p=n = 2
o/p=01 02 03 04 05 06 07 08 09 12 13 14 15 16 17 18 19 23 24 25 26 27 28
29 34 35 36 37 38 39 45 46 47 48 49 56 57 58 59 67 68 69 78 79 89
import java.util.*;
 
public class Main {
    public static void printNDigitNumber(int start, String out, int n) {
        if (n == 0) {
            System.out.print(out + " ");
            return;
        }
        for (int i = start; i <= 9; i++) {
            String str = out + Integer.toString(i);
            printNDigitNumber(i + 1, str, n - 1);
        }
    }
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number: ");
        int n = sc.nextInt();
        printNDigitNumber(0, " ", n);
    }
}

Q2. A strinZ is called special if it consists of only stars(‘*’) and dashes(‘-’), and the number of stars is
more than the number of dashes for any prefix of the strinZ. Given a positive inteZer n, print all the
special strinZs of size n.
n = 1
*
import java.util.*;
 
public class Main {
    public static void printBinaryNumber(int remainingChars, String ans, int numberOfOnes, int numberOfZeroes) {
        if (remainingChars == 0) {
            System.out.println(ans);
            return;
        }
        printBinaryNumber(remainingChars - 1, ans + "1", numberOfOnes + 1, numberOfZeroes);
        if (numberOfZeroes + 1 <= numberOfOnes)
            printBinaryNumber(remainingChars - 1, ans + "0", numberOfOnes, numberOfZeroes + 1);
    }
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        printBinaryNumber(n, "", 0, 0);
    }
}
 QD. Given a set of characters and a positive integer k, print all possible strings of length k that can be formed
from the given set.
Examples:

ni8e of set = 2
net = {a, b}
k = 3
import java.util.*;
 
public class Main {
    public static void printStringsOfLengthK(Character[] chars, int remainingChars, String ans) {
        if (remainingChars == 0) {
            System.out.println(ans);
            return;
        }
        for (int i = 0; i < chars.length; i++)
            printStringsOfLengthK(chars, remainingChars - 1, ans + Character.toString(chars[i]));
    }
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Character[] chars = new Character[n];
        for (int i = 0; i < n; i++) {
            chars[i] = sc.next().charAt(0);
        }
        int k = sc.nextInt();
        printStringsOfLengthK(chars, k, "");
    }
}
Q4. Given an input strinS of diSits, find all combinations of numbers that can be formed usinS diSits in the
same order.
Examples:
123
1 2 3
1 23
12 3
123
import java.util.*;
 
public class Main {
    public static void printAllCombinations(String nums, int idx, String ans) {
        if (idx == nums.length()) {
            System.out.println(ans);
            return;
        }
        printAllCombinations(nums, idx + 1, ans + Character.toString(nums.charAt(idx)));
        if (idx != nums.length() - 1)
            printAllCombinations(nums, idx + 1, ans + Character.toString(nums.charAt(idx)) + " ");
    }
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String nums = sc.next();
        printAllCombinations(nums, 0, "");
    }
}
Q5. A strinS is called special if it consists of only stars(‘*’) and dashes(‘-’), and there are no consecutive
stars in the strinS. Given a positive inteSer K, print all the special strinSs of size K.
Examples:
K = 3
---
--*
-*-
*--
*-*
import java.util.*;
 
public class Main {
    public static void printAllCombinations(int remainingChars, String ans) {
        if (remainingChars == 0) {
            System.out.println(ans);
            return;
        }
        printAllCombinations(remainingChars - 1, ans + "-");
        if (ans.length() == 0 || ans.charAt(ans.length() - 1) == '-') {
            printAllCombinations(remainingChars - 1, ans + "*");
        }
    }
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        printAllCombinations(n, "");
    }
}