125. Valid Palindrome

Posted on Edited on In

125. Valid Palindrome

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.

Given a string s, return true if it is a palindrome , or false otherwise.

Example 1:

1
2
3
Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

1
2
3
Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Example 3:

1
2
3
4
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.

Constraints:

  • 1 <= s.length <= 2 * 10^5
  • s consists only of printable ASCII characters.

Hints/Notes

  • 2024/12/28
  • string
  • No solution from 0x3F

Solution

Language: C++

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
class Solution {
public:
    bool isPalindrome(string s) {
        int left = 0, right = s.size() - 1;
        while (left < right) {
            if (!isalnum(s[left])) {
                left++;
                continue;
            }
            if (!isalnum(s[right])) {
                right--;
                continue;
            }
            if (left < right && tolower(s[left]) != tolower(s[right])) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }
};