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一、题目

125. Valid Palindrome

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.

题目来源： leetcode

二、题解

class Solution {
public:bool isPalindrome(string s) {int n = s.length();string tmp = "";for(int i = 0;i < n;i++){if(isdigit(s[i]) || isalpha(s[i])) tmp += s[i];}int i = 0,j = tmp.length() - 1;while(i < j){if(tolower(tmp[i]) != tolower(tmp[j])) return false;i++;j--;}return true;}
};