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82 lines
2.4 KiB
Plaintext
82 lines
2.4 KiB
Plaintext
---
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title: '125. Valid Palindrome'
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description: 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
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icon: dot
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topics:
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- { name: "Two Pointers", slug: "two-pointers" }
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- { name: "String", slug: "string" }
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video: "jJXJ16kPFWg"
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issue: "https://github.com/prdlk/leetcode/issues/41"
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companies:
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- { name: "tcs", period: "Thirty Days", frequency: 58.2 }
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- { name: "Meta", period: "Thirty Days", frequency: 53.8 }
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- { name: "Amazon", period: "Thirty Days", frequency: 39.1 }
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- { name: "Google", period: "Thirty Days", frequency: 29 }
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- { name: "Bloomberg", period: "Three Months", frequency: 79.9 }
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- { name: "Infosys", period: "Three Months", frequency: 66 }
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- { name: "Microsoft", period: "Three Months", frequency: 42.1 }
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- { name: "Deloitte", period: "Six Months", frequency: 81 }
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- { name: "Cognizant", period: "Six Months", frequency: 76.3 }
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- { name: "Axon", period: "Six Months", frequency: 75.4 }
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- { name: "Apple", period: "Six Months", frequency: 64.8 }
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sidebar:
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label: 'Valid Palindrome'
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badge: 'Easy'
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---
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### Example 1:
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- Input: `s = "A man, a plan, a canal: Panama"`
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- Output: `true`
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- Explanation: `"amanaplanacanalpanama"` is a palindrome.
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### Example 2:
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- Input: `s = "race a car"`
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- Output: `false`
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- Explanation: `"raceacar"` is not a palindrome.
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### Example 3:
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- Input: `s = " "`
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- Output: `true`
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- 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.
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### Constraints:
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- `1 <= s.length <= 2 * 10^5`
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- `s` consists only of printable ASCII characters.
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## Approach
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```mermaid
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flowchart TD
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S(["isPalindrome(s)"]) --> N["normal = s stripped of non-alphanumerics, lowercased"]
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N --> I["i = 0, j = normal.length - 1"]
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I --> W{"i < j?"}
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W -- no --> E(["return true — the pointers met in the middle"])
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W -- yes --> Q{"normal[i] != normal[j]?"}
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Q -- yes --> F(["return false"])
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Q -- no --> A["i++; j-- — step both inward"]
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A --> W
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```
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## Solution
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```js
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/**
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* @param {string} s
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* @return {boolean}
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*/
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var isPalindrome = function(s) {
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let normal = s.replace(/[^a-zA-Z0-9]/g, "").toLowerCase()
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let i = 0, j = normal.length - 1;
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while (i < j) {
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if(normal[i] !== normal[j]) {
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return false;
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}
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i++;
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j--;
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}
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return true;
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};
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```
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