# 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.

The original problem is here.

The original code is here.

# My Solution

I solve this problem in C++, as below:

``````/*
*Valid Palindrome
*Author: shuaijiang
*Email: zhaoshuaijiang8@gmail.com
*/
#include<iostream>
#include<vector>
#include<string.h>
#include<stdlib.h>
using namespace std;

class Solution {
public:
bool isPalindrome(string s) {
s = filter(s);
if(s.size() <=1)
return true;
int len = s.length();
for(int count=0;count<len/2;count++){
if(s[count] != s[len-count-1])
return false;
}
return true;
}

string filter(string s){
if(s == "")
return s;
int len = s.length();
string str;
for(int count=0;count<len;++count){
char  ch = s[count];
if(ch>='A'&&ch<='Z')
str.push_back(ch+32);
else if((ch>='a'&&ch<='z') || (ch>='0'&&ch<='9'))
str.push_back(ch);
}
return str;
}
};
//The codes under below is used for test
int main(){
string str("aa");
Solution s;
string filter_str = s.filter(str);
cout<<"Filter="<<filter_str<<endl;
bool isP = s.isPalindrome(str);
cout<<"isPalindrome="<<isP<<endl;
system("pause");
return 0;
}
``````

# Note

To solve the problem, first we should filter the string except alphanumeric characters. Then, we can compare the characters the two point of the string.