Question:

Consider the following Java method:

public static int[] manipulateArray(int[] arr) {
    int n = arr.length;
    int[] result = new int[n];
    
    // Traverse the array and double each element
    for (int i = 0; i < n; i++) {
        result[i] = arr[i] * 2;
    }
    
    // Reverse the elements in the array
    for (int i = 0, j = n - 1; i < j; i++, j--) {
        int temp = result[i];
        result[i] = result[j];
        result[j] = temp;
    }
    
    return result;
}

Explain what the manipulateArray method does and provide step-by-step explanation of the algorithm.

Answer:

The manipulateArray method takes an input array arr as a parameter and performs two operations on it: doubling each element and reversing the order of elements. Finally, it returns a new array with the manipulated elements.

Here is the step-by-step explanation of the algorithm:

1. Firstly, it initializes a variable n with the length of the input array arr. This will be used later for array traversal.

2. Then, it creates a new array result of the same length as the input array using int[] result = new int[n].

3. Next, it traverses the input array arr using a for loop from index 0 to n-1:

   a. Inside the loop, it multiplies each element arr[i] by 2 and stores the result in the corresponding index of the result array with result[i] = arr[i] * 2. This doubles each element in the array.

4. After doubling each element, the method performs the reverse operation on the result array. It uses a separate for loop that iterates from index 0 to n/2:

   a. Inside the loop, it swaps the elements at index i and n-i-1 using a temporary variable temp. This effectively reverses the order of elements in the array.

5. Finally, the method returns the manipulated result array.

This algorithm ensures that the input array is modified by doubling each element and reversing the order, and it returns the resultant array.