Leetcode Algorithms -- Valid Palindrome

Valid Palindrome (Easy)

Description

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

For example,
“A man, a plan, a canal: Panama” is a palindrome.
“race a car” is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

Analysis

简单字符串模拟

My Solution

//C++
class Solution {
    bool isok(char c){
        if(c>='A'&&c<='Z')
            return true;
        if(c>='a'&&c<='z')
            return true;
        if(c>='0'&&c<='9')
            return true;
        return false;
    }
    string trim(string s){
        string ans;
        for(int i = (int)s.length()-1;i>=0;i--){
            if(!isok(s[i]))
                continue;
            if(s[i]>='A'&&s[i]<='Z')
                s[i] = s[i]-'A'+'a';
            ans+=s[i];
        }
        return ans;
    }
public:
    bool isPalindrome(string s) {
        string ans = trim(s);
        int len = ans.length();
        for(int i=0;i<len/2;i++){
            if(ans[i]!=ans[len-i-1])
                return false;
        }
        return true;
    }
};