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125 Valid Palindrome.js

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// Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

// For example,

// "A man, a plan, a canal: Panama" is a palindrome.

// "race a car" is not a palindrome.

// Note:

// Have you consider that the string might be empty? This is a good question to ask during an interview.

// For the purpose of this problem, we define empty string as valid palindrome.

// Hide Company Tags Microsoft Uber Facebook Zenefits

// Hide Tags Two Pointers String

// Hide Similar Problems (E) Palindrome Linked List

/**

* @param {string} s

* @return {boolean}

*/

var isPalindrome = function(s) {

s = s.toLowerCase();

var beg = 0;

var end = s.length - 1;

while(beg < end) {

if(!s[beg].match(/[a-z0-9]/)) {

beg++;

} else if(!s[end].match(/[a-z0-9]/)) {

end--;

} else if(s[beg] !== s[end]) {

return false;

} else {

end--;

beg++;

}

}

return true;

};

/**

* @param {string} s

* @return {boolean}

*/

var isPalindrome = function(s) {

var head = 0;

var tail = s.length - 1;

s = s.toLowerCase();

while(head < tail) {

while(s[head] && !s[head].match(/[a-z0-9]/)) {

head++;

}

while(s[tail] && !s[tail].match(/[a-z0-9]/)) {

tail--;

}

if(head < tail && s[head] !== s[tail]) {

return false;

}

head++;

tail--;

}

return true;

};