题目

地址

https://leetcode.com/problems/valid-palindrome/description/

内容

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:

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.

Example 3:

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 * 105
• s consists only of printable ASCII characters.

解题

这题就是要检测字符串中字符和字母是否是回文。这样我们就要过滤掉所有不是数字和字母的内容，然后去比较。
解题的思路也很简单：两个方向相向而行，然后过滤掉所有不是数字和字母的，只要发现不符合回文特点就返回false。当两个方向下标相遇后，就说明对比结束。如果此时还没返回false，说明内容符合回文特点。

代码地址

https://github.com/f304646673/leetcode/tree/main/125-Valid-Palindrome