Why does the following Clojure not detect a palindrome?

Question

I'm just trying to convert to a string and compare to the reverse

(defn is-palindrome? [num]
  (= (str num) (reverse (str num))))

Something like

(is-palindrome 1221)

Is returning false

Answer 1

Try this instead:

(defn is-palindrome? [num]
  (= (str num) (apply str (reverse (str num)))))

In your code, the expression (reverse (str 1221)) returns the list of characters (\1 \2 \2 \1), which needs to be turned back into a string for the comparison to work. Alternatively, you could convert both numbers to character lists and perform a list comparison instead:

(defn is-palindrome? [num]
  (= (seq (str num)) (reverse (str num))))