I need to write a program that defines whether a string is a PALINDROME or not WITHOUT using fliplr, reverse or similar commands. Can anyone help with that ?

A palindrome is a word that remains the same when all of its letters are reversed: for example, ‘radar’ and ‘tenet’ are both palindromes. Write a program which asks the user to input a word and then checks whether it is a palindrome or not, and prints ‘True’ when it is, and ‘False’ when it is not. Do not use ‘fliplr’ (or similar commands/functions to ‘fliplr’ like ‘reverse’). Your program should make some checks whether the input is appropriate (e.g. whether the input is of character type or not).

Answer 1

[Jim Riggs]

A palindrome is a word or phrase that is exactly the same forward and bacward. I would use a loop to compare the first character to the last character, then the second character to the next to last character, etc. If all characters match like this, then it is a palindrome. (Note that you need to eliminate whte spaces from the string first)

[KIM QUOC ANH]

Is it possible to use index ?

[Jim Riggs]

Yes, absolutely.

Based on the instructions, above, your program should perform the following steps;

1: prompt the user to input a string

2) Verify that the input is a string

3) Check the string for white spaces and remove them (Note that a palindrome can be composed of more than one word. When this is the case, you need to remove white spaces between words. Even if you are only working with a single word, the user might input a space either in front of or after the word, which would cause your character-by-character test to fail, so checking for white spaces is a good idea)

4) Test the characters in the string for symmetry; (assume n characters after removing white spaces)

Character 1 is the same as character n

Character 2 is the same as character n-1

... etc.

This would be done in a loop such as:

n = length(string);
m = floor (n/2)
palendrome = true;
for i=1:m
  if string(i) ~= string (n+1-i)
     palendrome = false;
     break
  end
end
% At this point, the logical "palendrome" is True if the string is a palendrome

Note that step 3 can also be done in a loop.

Give it a try

[Guillaume]

The check can easily be carried out in one line without using any loop or function other than basic indexing and isequal. However, since this is homework, whose whole point is for the student to come up with their own algorithm, I'm not going to show how.

I just wanted to point out that using string as a variable name is a very bad idea, since it's also a built-in function (since R2016b).

[Jim Riggs]

I just checked google for some examples of palendromes, and ones that use multiple words also may contain punctuation, (which is ignored). So, step 3 should test for any non-alphabetic character and eliminate it from the string, not just white space) (see Matlab command isletter)