Technical Interview Question of the Day (5/11/12)

question

Create a method that checks if an input integer is a palindrome without using an array or converting it to a String.

ex. isPalindrome(1234) returns false

ex 2. isPalindrome(12321) returns true

show hint

Try playing with the modulus operator to extract digits.

show answer


				isPalindrome(input)
					
    reverse = 0;
					
    inTemp = input;
					

					
    while ( inTemp != 0 )
						
       reverse = (reverse * 10) + (inTemp % 10)
						
       inTemp = inTemp / 10
					

					
    if ( reverse == input )
						
       print("true")
					
    else
						
       print("false")

This solution works by first extracting the rightmost digit from the input number (ex. 1234 % 10 = 4) and then adding it to the current reversed number multiplied by ten (ex. (0 * 10) + 4 = 4; in second iteration (4 * 10) + (123 % 10) = 43). inTemp which initially stores the input number is divided by ten with each iteration to move on to the next digit. These steps are repeated until inTemp = 0 at which point all digits have been stored in reverse.