Valid palindrome-125,Lecture 22

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.

class Solution {
    private:
    bool valid(char ch){
        if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z')||(ch>='0'&&ch<='9')){
            return 1;
        }
        else {
            return 0;
        }
    }
    
     char lowercase(char ch){
        if((ch>='a'&&ch<='z')||(ch>='1'&&ch<='9')){
            return ch;
        }else{
            char temp= ch-'A'+'a';
            return temp;
        }
           }
public:
   


    bool isPalindrome(string s) {
        string temp="";
        for(int j=0;j<s.size();j++){
            if(valid(s[j])){
                temp.push_back(s[j]);
            }
        }
        for(int i=0;i<temp.size();i++){
        temp[i]=lowercase(temp[i]);
        }
        
        int st=0;int end=temp.size()-1;
        while(st<=end){
            if(temp[st]!=temp[end]){
                return 0;
            }else{
                st++;
                end--;
            }
        }
        return 1;
    }
};