palindrome.js

// in this example we don't need Math.floor, we just check i < j

function isPalindrome(phrase){
  alpha = [];
  for (var char of phrase.toLowerCase()) {
    if ('a' <= char && 'z' >= char) {
      alpha.push(char);
    }
  }
  phrase = alpha.join('');
  var j = phrase.length - 1;
  for (var i = 0; i < j; i++, j--) {
    if (phrase[i] !== phrase[j]) {
      return false
    }
  }
  return true;
}

palindrome.py

# in this verison, we create an unsafe palindrome checker which remarkably,
# works on every word in the english language I could find

def palindrome(s):
	return s == s[::-1]

def unsafe(s):
	if s[0] != s[-1]:
		return False
	n = len(s)
	return n <= 3 or s[1] == s[-2] and (n <= 5 or n <= 7 and s[2] == s[-3])

words = open('dict.txt').read().splitlines()
assert(map(unsafe, words) == map(palindrome, words))
from timeit import timeit

print(timeit("list(map(palindrome,words))",setup="from __main__ import words, palindrome", number=100))
print(timeit("list(map(unsafe,words))",setup="from __main__ import words, unsafe", number=100))
print(timeit("list(map(bool,words))",setup="from __main__ import words, unsafe", number=100))

#	palindrome	6.2 seconds
#	unsafe		4.2 seconds
#	bool		1.8 seconds (theoretic optimum?)