A 'array palindrome' is an array which, when its elements are reversed, remains the same (i.e., the elements of the array are sa
me when scanned forward or backward) Write a recursive, boolean-valued method, isPalindrome, that accepts an integer-valued array, and a pair of integers representing the starting and ending indexes of the portion of the array to be tested for being a palindrome. The function returns whether that portion of the array is a palindrome. An array is a palindrome if: the array is empty (0 elements) or contains only one element (which therefore is the same when reversed), or the first and last elements of the array are the same, and the rest of the array (i.e., the second through next-to-last elements) form a palindrome.
1 answer:
Answer:
Here is the JAVA program:
class Main {
static boolean isPalindrome(int array[], int starting, int ending) { /*a boolean method that takes an integer-valued array, and a pair of integers representing the starting and ending indexes of the portion of the array to be tested for being a palindrome */
if (starting >= ending) { //base case
return true; } //returns true
if (array[starting] == array[ending]) { //recursive case
return isPalindrome(array, starting + 1, ending - 1); } //calls isPalindrome recursively to find out palindrome
else {
return false; } } //returns false if array is not palindrome
public static void main (String[] args) { //start of main function
int array[] = { 1,2,3,2,1}; //creates an array
int size = array.length; //computes the size of array
System.out.print(isPalindrome(array, 0, size - 1)); } } //calls method to test array for being a palindrome
Explanation:
The program works as follows:
array = { 1,2,3,2,1}
starting = 0
ending = size-1 = 5-1 = 4
if (starting >= ending) condition evaluates to false because starting i.e. 0 is not greater or equal to ending i.e. 4. So the program moves to the next if part
if (array[starting] == array[ending])
This becomes:
if (array[0] == array[4])
The element at 0th index is the first element of the array i.e. 1 and the element at 4th index of array is the last element of array i.e. 1. So both these elements are equal so the following statement executes:
return isPalindrome(array, starting + 1, ending - 1);
Now the starting and ending become:
starting+1 = 0+1 = 1
ending-1 = 3
if (starting >= ending) base condition evaluates to false because starting is not greater or equal to ending. So the program moves to the next if part
if (array[starting] == array[ending])
This becomes:
if (array[1] == array[3])
The element at 1st index is 2 and the element at 3rd index of array is 2. So both these elements are equal so the following statement executes:
return isPalindrome(array, starting + 1, ending - 1);
Now the starting and ending become:
starting+1 = 1+1 = 2
ending-1 = 2
if (starting >= ending) base condition evaluates to true because starting is equal to ending. So the following statement executes:
return true;
This means the function returns true and this shows that array is a palindrome.
The screenshot of the program and its output is attached.
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Answer:
The program in cpp for the given scenario is shown below.
#include <stdio.h>
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
//object created of file stream
ofstream out;
//file opened for writing
out.open("numbers.txt");
std::cout << "File opened." << std::endl;
//inside for loop, random numbers written to numbers.txt using rand()
for(int n=0; n<10; n++)
{
out<<rand()<<endl;
}
//file closed
out.close();
std::cout << "File closed." << std::endl;
return 0;
}
Explanation:
1. An object of the ofstream is created. The ofstream refers to output file stream. This is used to create file for write and append operations.
ofstream out;
2. The file named, numbers.txt, is opened using the open() method with the object of ofstream.
out.open("numbers.txt");
3. The message is displayed to the user that the file is opened.
4. Inside a for loop, which executes 10 times, a random number is generated. This random number is written to the file and a new line inserted.
5. The random number is generated using rand() method. Every number is written on new line.
out<<rand()<<endl;
6. Every execution of the for loop repeats steps 4 and 5.
7. When the loop ends, the file is closed using close() method with the object of ofstream.
out.close();
8. A message is displayed to the user that the file is closed.
9. The header file, fstream, is included to support file operations.
10. The extension of the file can be changed from .txt to any other type of file as per requirement.
11. The program can be tested for writing more numbers to the file.
12. The program can be tested for writing any type of numeric data to the file.
13. The program is written in cpp due to simplicity.
14. In other languages such as java or csharp, the code is written inside classes.
15. In cpp, all the code is written inside main() method.
16. The screenshot of the output messages displayed is attached.
