java dsa-recursion

Recursion/DisplayNNumbers.java

@@ -0,0 +1,36 @@
+package Java_DSA.Recursion;
+import java.util.Scanner;
+
+public class DisplayNNumbers
+{
+    public static void printDescending(int n)
+    {
+        if(n==0)
+            return;
+        System.out.print(n + " ");
+        printDescending(n-1);
+    }
+
+    public static void printAscending(int n)
+    {
+        if(n==0)
+            return;
+        printAscending(n-1);
+        System.out.print(n + " ");
+    }
+
+    public static void main(String[] args)
+    {
+        Scanner scan = new Scanner(System.in);
+        int n;
+        System.out.println("Enter value of n : ");
+        n = scan.nextInt();
+
+        printDescending(n);
+        System.out.println();
+
+        printAscending(n);
+        System.out.println();
+
+    }
+}

Recursion/Factorial.java

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+package Java_DSA.Recursion;
+import java.util.*;
+
+public class Factorial
+{
+    public static int calcFactorial(int n){
+        if(n == 1){
+            return 1;
+        }
+        int fact = calcFactorial(n-1);
+        int ans = n * fact;
+        return ans;
+    }
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the value of n : ");
+        int n = sc.nextInt();
+        int result = calcFactorial(n);
+        System.out.println(result);
+    }
+}

Recursion/Fibonacci.java

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+package Java_DSA.Recursion;
+import java.util.*;
+
+public class Fibonacci {
+   public static void fibonacci(int i,int n,int n1,int n2){
+       if(i == n){
+         return;
+       }
+       int n3 = n1 + n2;
+       System.out.println(n3);
+       n1 = n2;
+       n2 = n3;
+       fibonacci(i+1,n,n1,n2);
+
+   }
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the value of n : ");
+        int n = sc.nextInt();
+        int n1 = 0;
+        int n2 = 1;
+        System.out.println(0);
+        System.out.println(1);
+        fibonacci(2,n,n1,n2);
+
+    }
+}

Recursion/StringPermutation.java

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+package Java_DSA.Recursion;
+
+public class StringPermutation {
+    public static void calcPermutation(String str,String perm,int index){
+        if(str.length() == 0){
+            System.out.println(perm);
+            return;
+        }
+        for(int i = 0;i < str.length();i++){
+               char currChar = str.charAt(i);
+               String newStr = str.substring(0,i) + str.substring(i+1);
+               calcPermutation(newStr,perm + currChar,index+1);
+           }
+    }
+    public static void main(String[] args) {
+        String str = "ABC";
+        calcPermutation(str,"",0);
+    }
+}

Recursion/SumOfNNumbers.java

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+package Java_DSA.Recursion;
+import java.util.Scanner;
+
+public class SumOfNNumbers
+{
+    public static void calculateSum(int i ,int n,int sum){
+        if(i == n){
+            sum = sum + i;
+            System.out.println(sum);
+            return;
+        }
+        sum = sum + i;
+        calculateSum(i+1,n,sum);
+    }
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the value of n : ");
+        int n = sc.nextInt();
+        calculateSum(1,n,0);
+    }
+}