Recursion for Coding Interviews in Java/

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Direct vs. Indirect Recursion

Direct vs. Indirect Recursion

This lesson explains two different types of recursion: direct and indirect recursion.

We'll cover the following...

Direct Recursion

Direct recursion occurs when a method calls itself.

This results in a one-step recursive call: the method makes a recursive call inside its own body.

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class ExampleClass {
  private static void f() {
    
    // some code...
    f();
    //some code...
  }
  public static void main(String args[] ) {
    // Method called here
  }
}

The code snippet below gives an example of a direct recursive method that computes the square of a number.

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class Square {
    // Recursive method to calculate square of a number
    private static int square(int n) {
        // Base case
        if (n == 0) {
            return 0;
        }
        // Recursive case
        else {
            return square(n-1) + (2 * n) - 1;
        }
    }
    public static void main( String args[] ) {
        int input = 6;
        int output = square(input);
        System.out.println("The square of the number " + input + " is: " + output);
    }
}

We will now briefly discuss the two main parts of a recursive method, the base case and the recursive case, implemented in the code above.

The Base Case

We have defined the base case on line 5 where it states that when the variable n equals to 00, the method should terminate and start popping frames from the stack.

The Recursive Case

Let’s take a look at the mathematical operation required to perform n2n^2. We need to decrement the value of n in such a way that we can use it to call the same method but not change the mathematical formula. We get this:

(n−1)2 ...