MATLAB: I’m trying to create a code that determines whether a word (or phrase) is a palindrome. The code only needs to look at the actual letters within the input string, but I’m not sure how to do that.

for looploopspalindrome

The jist of the problem is to create a function that determines whether a string input is a palindrome by returning the logical true or false. The function needs to disregard any non-letter (i.e. punctuation, spaces, capitalization, etc.), but I'm not sure how to do this.

Here is my code:

function palindrome = hw4_problem2(v)
palindrome = true;
l = lower(v);
n = length(v);
if mod(n, 2) == 0
    for ii = 1:n
        for jj = n:-1:1
            if l(ii) ~= l(jj)
                palindrome = false;
            else
                palindrome = true;
            end
        end
    end
end
end

I was able to use "lower" to get everything into lower letter form, but how do I disregard nonletters? Thanks.

Best Answer

Well, you did show some effort, actually a credible one at that. :) You already know how to use tools like lower, so try a few others.

str = 'The quick Brown fox jumped over the lazy dog.';
str = lower(str);
str = str(ismember(str,'abcdefghijklmnopqrstuvwxyz'))
str =
    'thequickbrownfoxjumpedoverthelazydog'

Now how can you tell if it is a palindrome? Have you considered flip?

isequal(str,flip(str))
ans =
  logical
   0

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MATLAB: Outputting cell vectors that contain specific information help

You can use the colon operator to generate a character vector containing each lower case letter in the alphabet:

>> 'a':'z'
ans =
    'abcdefghijklmnopqrstuvwxyz'

Same with upper case letters:

>> 'A':'Z'
ans =
    'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

Or this, if you want:

>> 'A':'z'
ans =
    'ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz'

See here for more info. You can use double() and char() to switch between number and corresponding character:

>> double('a')
ans =
    97
>> char(97)
ans =
    'a'

So, 'a':'z' is kind of like

>> char(double('a'):double('z'))
ans =
    'abcdefghijklmnopqrstuvwxyz'

When you compare characters,

>> 'a' < 'z'
ans =
  logical
   1

this is like

>> double('a') < double('z')
ans =
  logical
   1

or rather

>> 97 < 122
ans =
  logical
   1

In your professor's code:

str >= 'A' & str <= 'Z'

Here, each character within str is being compared to 'A' and 'Z'. The output is a logical array with the same size as str, containing a 1 where the corresponding character of str is between 'A' and 'Z' (i.e. somewhere within the array 'A':'Z').

>> 'GHSIEVBSK' >= 'A' & 'GHSIEVBSK' <= 'Z'
ans =
  1×9 logical array
   1   1   1   1   1   1   1   1   1

Here, str has all capital letters, so every element in the output is true.

>> 'GhSIeVBsK' >= 'A' & 'GhSIeVBsK' <= 'Z'
ans =
  1×9 logical array
   1   0   1   1   0   1   1   0   1

Here, some characters in str are lower-case. The corresponding elements in the output are false. With

if sum(str >= 'A' & str <= 'Z') == length(str)

your professor is checking that every element in the output is a 1. Also valid would be

if all(str >= 'A' & str <= 'Z')

Take another look at the documentation for contains.

>> contains('abc', 'a':'z')
ans =
  logical
   0

This returns 0 because the entirety of 'a':'z' is not found within 'abc'. To check if any element of 'a':'z' is within 'abc', you could use for example

>> contains('abc', cellstr(('a':'z')')')
ans =
  logical
   1

Best Answer

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