A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.
Given a string s, return true if it is a palindrome, or false otherwise.
Example 1:
Input: s = "A man, a plan, a canal: Panama"
Output:
true
Explanation:
"amanaplanacanalpanama" is a palindrome.
Example 2:
Input: s = "race a car"
Output:
false
Explanation:
"raceacar" is not a palindrome.
Example 3:
Input: s = " "
Output:
true
Explanation:
s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.
Pseudocode
a valid palindrome is when the a str is a mirror image with the center letter/s as pivot.
- compare starting kth and ending kth letters
- need to clean up string to exclude whitespaces and other symbols and only include lowercase alphabets
- s.toLowerCase()
- use regular expression to replace everything that isn't numbers of alphabets to ""
- /[^0-9a-z]/g - explained in https://regexr.com/
Solution
var isPalindrome = function (s) {
let str = s.toLowerCase().replace(/[^0-9a-z]/g, "");
let start = 0;
let end = str.length - 1;
while (start < end) {
if (str[start] !== str[end]) {
return false;
}
start++;
end--;
}
return true;
};
Time and Space Complexity
Time
replace characters to lowercase - O(N)
regular expression to remove non alphanumeric characters - O(N)
loop through start and end simultaneously to compare characters - O(N)
