Oletem
10/1/2017 - 2:51 PM
Check for Palindromes
Return true if the given string is a palindrome. Otherwise, return false.
A palindrome is a word or sentence that's spelled the same way both forward and backward, ignoring punctuation, case, and spacing.
Note You'll need to remove all non-alphanumeric characters (punctuation, spaces and symbols) and turn everything lower case in order to check for palindromes.
We'll pass strings with varying formats, such as "racecar", "RaceCar", and "race CAR" among others.
We'll also pass strings with special symbols, such as "2A33a2", "2A3 3a2", and "2_A33#A2".
Remember to use Read-Search-Ask if you get stuck. Write your own code.
Here are some helpful links:
String.prototype.replace() String.prototype.toLowerCase()
function palindrome(str) {
var re = /[\W_]/g;
var lowRegStr = str.toLowerCase().replace(re, ''); /* берем эту бредовую исходную фразу
переводим ее в нижний реистр, заменям все спецсимволы, убираем пробелы.
ВОТ ТЕПЕРЬ МЫ МОЖЕМ РАЗВОРАЧИВАТЬ ИХ ВСПЯТЬ, ЧТОБЫ СРАВНИВАТЬ
при сравнении str === reverseStr - знаки, пробелы, прочее - не будут убраны из стринга
*/
var reverseStr = lowRegStr.split('').reverse('').join('');
return lowRegStr === reverseStr;
}
palindrome("My age is 0, 0 si ega ym.");
/* -------------------------------------------- With a FOR loop -------------------------------*/
function palindrome(str) {
// Step 1. The first part is the same as earlier
var re = /[^A-Za-z0-9]/g; // or var re = /[\W_]/g;
str = str.toLowerCase().replace(re, '');
// Step 2. Create the FOR loop
var len = str.length; // var len = "A man, a plan, a canal. Panama".length = 30
for (var i = 0; i < len/2; i++) {
if (str[i] !== str[len - 1 - i]) { // As long as the characters from each part match, the FOR loop will go on
return false; // When the characters don't match anymore, false is returned and we exit the FOR loop
}
/* Here len/2 = 15
For each iteration: i = ? i < len/2 i++ if(str[i] !== str[len - 1 - i])?
1st iteration: 0 yes 1 if(str[0] !== str[15 - 1 - 0])? => if("a" !== "a")? // false
2nd iteration: 1 yes 2 if(str[1] !== str[15 - 1 - 1])? => if("m" !== "m")? // false
3rd iteration: 2 yes 3 if(str[2] !== str[15 - 1 - 2])? => if("a" !== "a")? // false
4th iteration: 3 yes 4 if(str[3] !== str[15 - 1 - 3])? => if("n" !== "n")? // false
5th iteration: 4 yes 5 if(str[4] !== str[15 - 1 - 4])? => if("a" !== "a")? // false
6th iteration: 5 yes 6 if(str[5] !== str[15 - 1 - 5])? => if("p" !== "p")? // false
7th iteration: 6 yes 7 if(str[6] !== str[15 - 1 - 6])? => if("l" !== "l")? // false
8th iteration: 7 yes 8 if(str[7] !== str[15 - 1 - 7])? => if("a" !== "a")? // false
9th iteration: 8 yes 9 if(str[8] !== str[15 - 1 - 8])? => if("n" !== "n")? // false
10th iteration: 9 yes 10 if(str[9] !== str[15 - 1 - 9])? => if("a" !== "a")? // false
11th iteration: 10 yes 11 if(str[10] !== str[15 - 1 - 10])? => if("c" !== "c")? // false
12th iteration: 11 yes 12 if(str[11] !== str[15 - 1 - 11])? => if("a" !== "a")? // false
13th iteration: 12 yes 13 if(str[12] !== str[15 - 1 - 12])? => if("n" !== "n")? // false
14th iteration: 13 yes 14 if(str[13] !== str[15 - 1 - 13])? => if("a" !== "a")? // false
15th iteration: 14 yes 15 if(str[14] !== str[15 - 1 - 14])? => if("l" !== "l")? // false
16th iteration: 15 no
End of the FOR Loop*/
}
return true; // Both parts are strictly equal, it returns true => The string is a palindrome
}
palindrome("A man, a plan, a canal. Panama");