Question

Write a short C++ function that repeatedly selects and removes a random entry from an n-element array until the array holds no more entries. Assume that you have access to a function random(k), which returns a random integer in the range from 0 to k.

Short answer

A C++ function iteratively removes random entries from an array until it is empty.

Step-by-step solution

- Create Function Skeleton

Create the skeleton of a C++ function named `removeRandomEntries`. This function will take an integer array and its size as parameters.

- Set Up Loop

Inside the function, set up a while loop that continues as long as the array size is greater than 0.

- Generate Random Index

Within the loop, use the given `random(k)` function to generate a random index between 0 and the current array size minus one.

- Remove Entry

Remove the entry at the random index by shifting all subsequent entries one position to the left, effectively overwriting the random entry.

- Decrease Array Size

After removing the entry, decrease the array size by one to reflect the removal.

- End Function

Once the loop terminates (when the array is empty), end the function.

Key concepts

C++ function

Understanding how to write a C++ function is fundamental to solving this exercise.
A function in C++ is a block of code designed to perform a specific task. In this case, our task is to repeatedly remove random entries from an array.
The general structure of a function in C++ includes:

• A return type indicating what type of value, if any, the function will return. For instance, using `void` means the function does not return any value.
• A function name, which in this case is `removeRandomEntries`.
• Parameters, which are inputs to the function. Here, the parameters include the integer array and its size.

Below is a basic skeleton of the function: ```cpp void removeRandomEntries(int arr[], int &n) { // Function implementation } ```
The parameter `int &n` is passed by reference, meaning any modification to `n` within the function reflects outside the function as well. Understanding this concept is crucial in array manipulation.

array manipulation

Array manipulation involves actions like adding, removing, sorting, or updating elements in an array. In this exercise, the primary task is to remove an entry from the array and adjust the remaining elements.
Here are the steps for removing an entry from an array:

• Identify the index of the element to be removed.
• Shift all subsequent elements one position to the left to fill the gap created by the removed element.

Consider the following array: `int arr[] = {4, 7, 2, 5};`. If we remove the element at index 1 (value 7), we need to shift the elements to get `{4, 2, 5}`.`
In C++, this can be done using a simple loop inside our function: ```cpp for (int i = randomIndex; i < n - 1; i++) { arr[i] = arr[i + 1]; } n--; ```
This loop starts from the index of the removed element and shifts each subsequent element leftwards, effectively removing the desired entry and reducing the size of the array by one.

random number generation

Generating random numbers is a common task in programming, and C++ provides several ways to do this. In our exercise, we need to generate a random index to select an entry for removal.
The provided `random(k)` function returns a random integer between 0 and `k`. To use this in our function, we first ensure that we correctly pass the range. Suppose `n` is the current size of the array: ```cpp int randomIndex = random(n - 1); ```
C++ has built-in functions for random number generation in the header ``. To get similar functionality, you might use: ```cpp #include int randomIndex = rand() % n; ```
Here, `rand()` generates a random number, and the modulo operator (`%`) ensures that the number falls within the range of 0 to `n-1`. Combining this with our array manipulation, you can see how we can effectively select and remove random entries from an array until it becomes empty.