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| 1 | +/** |
| 2 | + * @param {string} s |
| 3 | + * @return {boolean} |
| 4 | + */ |
| 5 | + |
| 6 | +/** |
| 7 | + * @param {strng} s string to check if palindrome |
| 8 | + * @return {boolean} True if string is a palindrome (only counting alphanumeric chars). |
| 9 | + * @summary Valid palindrome {@link https://leetcode.com/problems/valid-palindrome/} |
| 10 | + * @description Given an input string, return true if its a palindrome (non-alphanumeric chars excluded); |
| 11 | + * Space O(1) - No extra space (few variables). |
| 12 | + * Time O(n) - Traverse over the input string. |
| 13 | + */ |
| 14 | +const isPalindrome = s => { |
| 15 | + if (!s) return true; |
| 16 | + |
| 17 | + const isAlphanumeric = c => |
| 18 | + (code >= 'a'.charCodeAt() && code <= 'z'.charCodeAt()) || (code >= '0'.charCodeAt() && code <= '9'.charCodeAt()); |
| 19 | + |
| 20 | + let left = 0; |
| 21 | + let right = s.length - 1; |
| 22 | + const mid = Math.ceil(s.length / 2); |
| 23 | + |
| 24 | + while (left <= right) { |
| 25 | + const leftChar = s[left].toLowerCase(); |
| 26 | + const rightChar = s[right].toLowerCase(); |
| 27 | + |
| 28 | + const isLeftValid = isAlphanumeric(leftChar.charCodeAt()); |
| 29 | + const isRightValid = isAlphanumeric(rightChar.charCodeAt()); |
| 30 | + |
| 31 | + if (isLeftValid && isRightValid && leftChar !== rightChar) return false; |
| 32 | + |
| 33 | + if (!isLeftValid && isRightValid) left++; |
| 34 | + else if (isLeftValid && !isRightValid) right--; |
| 35 | + else { |
| 36 | + left++; |
| 37 | + right--; |
| 38 | + } |
| 39 | + } |
| 40 | + |
| 41 | + return true; |
| 42 | +}; |
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