Add palindrome (#281)

Author: ITZ-NIHALPATEL

DIRECTORY.md

@@ -85,6 +85,7 @@
   * [Fibonacci](https://github.com/TheAlgorithms/R/blob/HEAD/mathematics/fibonacci.r)
   * [First N Fibonacci](https://github.com/TheAlgorithms/R/blob/HEAD/mathematics/first_n_fibonacci.r)
   * [Greatest Common Divisor](https://github.com/TheAlgorithms/R/blob/HEAD/mathematics/greatest_common_divisor.r)
+  * [Palindrome Check](https://github.com/TheAlgorithms/R/blob/HEAD/mathematics/isPalindrome.r)
   * [Josephus Problem](https://github.com/TheAlgorithms/R/blob/HEAD/mathematics/josephus_problem.r)
   * [Least Common Multiple](https://github.com/TheAlgorithms/R/blob/HEAD/mathematics/least_common_multiple.r)
   * [Modular Exponentiation](https://github.com/TheAlgorithms/R/blob/HEAD/mathematics/modular_exponentiation.r)

mathematics/isPalindrome.r

@@ -0,0 +1,39 @@
+#' Check if a number is a palindrome
+#'
+#' @description Checks if an integer is a palindrome (reads the same forwards
+#'   and backward) without using strings. Negative numbers are not palindromes.
+#' @param number The integer to check.
+#' @return TRUE if the number is a palindrome, FALSE otherwise.
+#' @examples
+#' isPalindrome(121)
+#' isPalindrome(123)
+
+isPalindrome <- function(number) {
+  # Negative numbers are not considered palindromes
+  if (number < 0L) {
+    return(FALSE)
+  }
+
+  original_number <- number
+  reversed_number <- 0L
+
+  # Loop while the number is greater than 0
+  while (number > 0L) {
+    # Get the last digit
+    remainder <- number %% 10L
+    
+    # Build the reversed number
+    reversed_number <- (reversed_number * 10L) + remainder
+    
+    # Remove the last digit using integer division
+    number <- number %/% 10L
+  }
+
+  # Return TRUE if the original and reversed numbers are the same
+  return(original_number == reversed_number)
+}
+
+isPalindrome(121)
+isPalindrome(123)
+isPalindrome(7)
+isPalindrome(-101)