125. Valid Palindrome

Ignoring case and non-alphanumeric characters, return true if s reads the same forward and backward.

Move lo and hi toward each other, skipping non-alphanumeric characters, and compare lowercase characters.

1function isPalindrome(s: string): boolean {
2  let lo = 0, hi = s.length - 1;
3  while (lo < hi) {
4    if (!/[a-z0-9]/i.test(s[lo])) { lo++; continue; }
5    if (!/[a-z0-9]/i.test(s[hi])) { hi--; continue; }
6    if (s[lo].toLowerCase() !== s[hi].toLowerCase()) return false;
7    lo++; hi--;
8  }
9  return true;
10}

s

␣

Pointers at both ends.

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