README_EN.md

125. Valid Palindrome

中文文档

Description

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

 

Example 1:

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

Example 2:

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

 

Constraints:

• 1 <= s.length <= 2 * 105
• s consists only of printable ASCII characters.

Solutions

Python3

class Solution:
    def isPalindrome(self, s: str) -> bool:
        i, j = 0, len(s) - 1
        while i < j:
            if not s[i].isalnum():
                i += 1
            elif not s[j].isalnum():
                j -= 1
            elif s[i].lower() != s[j].lower():
                return False
            else:
                i += 1
                j -= 1
        return True

Java

class Solution {
    public boolean isPalindrome(String s) {
        int i = 0, j = s.length() - 1;
        while (i < j) {
            if (!Character.isLetterOrDigit(s.charAt(i))) {
                ++i;
            } else if (!Character.isLetterOrDigit(s.charAt(j))) {
                --j;
            } else if (Character.toUpperCase(s.charAt(i)) != Character.toUpperCase(s.charAt(j))) {
                return false;
            } else {
                ++i;
                --j;
            }
        }
        return true;
    }
}

C++

class Solution {
public:
    bool isPalindrome(string s) {
        int i = 0, j = s.size() - 1;
        while (i < j) {
            if (!isAlphaNum(s[i])) ++i;
            else if (!isAlphaNum(s[j])) --j;
            else if ((s[i] + 32 - 'a') % 32 != (s[j] + 32 - 'a') % 32) return false;
            else {
                ++i;
                --j;
            }
        }
        return true;
    }

private:
    bool isAlphaNum(char &ch) {
        if (ch >= 'a' && ch <= 'z') return true;
        if (ch >= 'A' && ch <= 'Z') return true;
        if (ch >= '0' && ch <= '9') return true;
        return false;
    }
};

TypeScript

function isPalindrome(s: string): boolean {
    let left: number = 0,
        right: number = s.length - 1;
    while (left < right) {
        let char1: string = s.charAt(left);
        let char2: string = s.charAt(right);
        if (!/[a-zA-Z0-9]/.test(char1)) {
            ++left;
        } else if (!/[a-zA-Z0-9]/.test(char2)) {
            --right;
        } else if (char1.toLocaleLowerCase() != char2.toLocaleLowerCase()) {
            return false;
        } else {
            ++left;
            --right;
        }
    }
    return true;
}

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