Recursion

Author: ibhawanagaur

Data Structure and Algorithms/Recursion/binarySearch.java

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+/*Binary search using recursion*/
+
+package Recursion;
+
+public class binarySearch 
+{
+	public static int binarySearch(int a[],int si,int ei,int x)
+	{
+		if(si>ei)
+		{
+			return -1;
+	    }
+	    
+		int midIndex=(si+ei)/2;
+	    if(a[midIndex]==x)
+	    {
+	    	return midIndex;
+	    }
+	    else if(a[midIndex]<x)
+	    {
+	    	return binarySearch(a,midIndex+1,ei,x);
+	    }
+	    else
+	    {
+	    	return binarySearch(a,si,midIndex-1,x);
+	    }
+	} 
+	
+	public static void main(String[] args) 
+	{	
+		int[] a={1,3,4,5,6,8};
+        System.out.println(binarySearch(a,0,a.length-1,6));
+	}
+}

Data Structure and Algorithms/Recursion/calculatePower.java

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+/*Calculate Power
+Write a program to find x to the power n (i.e. x^n). Take x and n from the user.*/
+
+package Recursion;
+
+import java.util.Scanner;
+
+public class calculatePower 
+{
+	public static int calculatePower(int x, int n)
+	{
+		if(n == 0)
+		{
+			return 1;
+		}
+		int smallOutput = calculatePower(x, n-1);
+		int output = x*smallOutput ;
+		return output;
+	}
+	
+	public static void main(String[] args) 
+	{
+		Scanner sc = new Scanner(System.in);
+		System.out.print("Enter the number : ");
+		int number  = sc.nextInt();
+		System.out.print("Enter the power : ");
+		int power = sc.nextInt();
+		int answer = calculatePower(number, power);
+		System.out.print(number + "^"+ power +" = "+ answer);
+	}
+}

Data Structure and Algorithms/Recursion/checkAB.java

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+/*Check AB
+Suppose you have a string, S, made up of only 'a's and 'b's. Write a recursive function that checks if the string was generated using the following rules:
+a. The string begins with an 'a'
+b. Each 'a' is followed by nothing or an 'a' or "bb"
+c. Each "bb" is followed by nothing or an 'a'
+If all the rules are followed by the given string, return true otherwise return false.*/
+
+package Recursion;
+
+public class checkAB 
+{
+	public static boolean checkAb(String s)
+	{
+	    if (s.length()==0) {
+	    	return true;
+	    }
+	    
+	    if (s.charAt(0) != 'a'){
+	    	return false;
+	    }
+	    
+	    if (s.length() >= 3 && "abb".equals(s.substring(0,3))){
+	    	return checkAb(s.substring(3));
+	    }
+	    else 
+	    {
+	    	return checkAb(s.substring(1));
+	    }
+	}
+	
+	public static void main(String[] args) 
+	{		
+		System.out.println(checkAb("abababa"));	
+	}
+}

Data Structure and Algorithms/Recursion/checkArraySorted.java

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+/* Check if the array is sorted
+Given an array of length N, you need to find whether the array is sorted or not. */
+
+package Recursion;
+
+import java.util.Scanner;
+
+public class checkArraySorted 
+{
+	public static boolean isArraySorted(int arr[],int si)
+	{
+        if(si==arr.length-1)
+        {
+            return true;
+        }
+        if(arr[si]>arr[si+1])
+        {
+            return false;
+        }
+        boolean isSmallArraySorted=isArraySorted(arr,si+1);
+        return isSmallArraySorted;
+    }
+	
+//	public static boolean isArraySorted(int arr[])
+//	{
+//		if(arr.length == 1)
+//		{
+//			return true;
+//		}
+//		if(arr[0]>arr[1])
+//		{
+//			return false;
+//		}
+//		
+//		int smallArray[] = new int[arr.length-1];
+//		for(int i=1;i<arr.length;i++)
+//		{
+//			smallArray[i-1] = arr[i];
+//		}
+//			boolean isSmallArraySorted = isArraySorted(smallArray);
+//			return isSmallArraySorted;
+//	}
+	
+	public static void main(String[] arg)
+	{
+		Scanner sc = new Scanner(System.in);
+		System.out.print("Enter the size of array : ");
+		int size = sc.nextInt();
+		int[] input_arr = new int[size];
+		
+		for(int i=0; i<size; i++)
+		{
+			System.out.print("Enter the element at "+ i + "th term : ");
+			input_arr[i] = sc.nextInt();
+		}
+		
+		for(int i= 0; i<size; i++)
+		{
+			System.out.print(input_arr[i]+ ", ");
+		}
+		System.out.println();
+		
+		//System.out.println(isArraySorted(input_arr));
+		System.out.println(isArraySorted(input_arr,0));
+	}
+}

Data Structure and Algorithms/Recursion/checkNumberInArray.java

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+/*Check Number in Array
+Given an array of length N and an integer x, you need to find if x is present in the array or not. Return true or false.
+Do this recursively.*/
+
+package Recursion;
+
+import java.util.Scanner;
+
+public class checkNumberInArray 
+{
+	public static boolean checkNumber(int arr[],int x) 
+	{	
+		int n = arr.length;
+		if (n <= 0) 
+		{
+			return false;
+        }
+		if(arr[0] == x)
+		{
+			return true;
+		}
+		
+		int smallArray[] = new int[n-1];
+		for(int i=1;i<n;i++)
+		{
+			smallArray[i-1] = arr[i];
+		}
+		
+		boolean smallOutput = checkNumber(smallArray,x);
+		
+		return smallOutput;
+    }
+	/*We can optimized the code
+	public static boolean checkNumber(int arr[], int x, int si)
+	{
+		if(arr[si]==x)
+		{
+			return true;
+		}
+		if(arr[si]!=x)
+		{
+			return false;
+		}
+		return checkNumber(arr, x , si+1);
+	}*/
+
+	public static void main(String[] arg)
+	{
+		Scanner sc = new Scanner(System.in);
+		System.out.print("Enter the size of array : ");
+		int size = sc.nextInt();
+		int[] input_arr = new int[size];
+		
+		System.out.print("Enter the number for search : ");
+		int x = sc.nextInt();
+		
+		for(int i=0; i<size; i++)
+		{
+			System.out.print("Enter the element at "+ i + "th term : ");
+			input_arr[i] = sc.nextInt();
+		}
+		
+		for(int i= 0; i<size; i++)
+		{
+			System.out.print(input_arr[i]+ ", ");
+		}
+		System.out.println();
+		
+		System.out.println(checkNumber(input_arr, x));
+		
+	}
+}

Data Structure and Algorithms/Recursion/checkPalindrome.java

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+/*Check Palindrome (recursive)
+Check whether a given String S is a palindrome using recursion. Return true or false.*/
+
+package Recursion;
+
+public class checkPalindrome 
+{
+	public static boolean Palindrome(String input) {
+		if(input.length()<=1)
+		{
+			return true;
+		}
+		else if(input.charAt(0)!=input.charAt(input.length()-1))
+		{
+			return false;	
+		}
+		return Palindrome(input.substring(1, input.length()-1));
+
+	}
+
+	public static void main(String[] args) 
+	{		
+		System.out.println(Palindrome("racecar"));	
+	}
+}

Data Structure and Algorithms/Recursion/countZeros.java

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+/*Count Zeros
+Given an integer N, count and return the number of zeros that are present in the given integer using recursion.*/
+
+package Recursion;
+
+import java.util.Scanner;
+
+public class countZeros 
+{
+	public static int count(int n)
+	{
+		if(n == 0)
+		{
+			return 1;
+		} 
+		
+		if(n<10)
+		{
+			return 0;
+		}
+		else if(n%10 == 0)
+		{
+			return 1 + count(n/10);
+		}
+		return count(n/10);
+	}
+	public static void main(String[] arg)
+	{
+		Scanner sc = new Scanner(System.in);
+		System.out.print("Enter the number : ");
+		int number = sc.nextInt();
+		
+		System.out.println("Total number of zeros in "+ number +" : "+count(number));
+	}
+}

Data Structure and Algorithms/Recursion/factorial.java

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+/*Factorial
+Write a program to calculate factorial of N number. Take n from the user.*/
+
+package Recursion;
+
+import java.util.Scanner;
+
+public class factorial 
+{
+	public static int fact(int number)
+	{
+		if(number == 0)
+		{
+			return 1;
+		}
+		int smallOutput = fact(number-1);
+		return number*smallOutput;
+	}
+	
+	public static void main(String[] args) 
+	{
+		System.out.print("Enter the number : ");
+		Scanner sc = new Scanner(System.in);
+		int number = sc.nextInt();
+		
+		int factorialN = fact(number);
+		System.out.print("factorial of "+ number +" is : "+ factorialN);
+	}
+}

Data Structure and Algorithms/Recursion/fibonacciNumber.java

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+/*FibonacciNumber 
+ Write a program to print nth number in fibonacci series*/
+
+package Recursion;
+
+import java.util.Scanner;
+
+public class fibonacciNumber 
+{
+	public static int Fibonacci(int number)
+	{
+		if(number == 1 || number == 2)
+		{
+			return 1;
+		}
+		
+		int f1 = Fibonacci(number-1);
+		int f2 = Fibonacci(number-2);
+		int output = f1 + f2;
+		return output;	
+	}
+	
+	public static void main(String[] args) 
+	{
+		Scanner sc = new Scanner(System.in);
+		System.out.print("Enter the number : ");
+		int number  = sc.nextInt();
+		System.out.print(Fibonacci(number));
+	}
+}