125. Valid Palindrome

📝 Problem Details

• Title: 125. Valid Palindrome
• Link: https://leetcode.com/problems/valid-palindrome/
• Difficulty: Easy
• Tags/Categories: Two-Pointers Strings

input string s return true if s is a palindrome, false otherwise

💡 Explanation of Solution

- two pointers approach 
	- i set to the start of the string
	- j set to the end of the string
	- move them closer each iteration
	- have two nested while loops to prevent non-alphanumeric characters from breaking the two pointers comparison 

⌛ Complexity Analysis

Time Complexity: O(n)
Space Complexity: O(1)

💻 Implementation of Solution

class Solution {
public:
    bool isPalindrome(string s) {
        int i = 0;
        int j = s.size()-1;
 
        while(i < j) {
            while(!isalnum(s[i]) && i < j) i++;
            while(!isalnum(s[j]) && i < j) j--;
 
            if(tolower(s[i]) != tolower(s[j]))
                return false;
 
            i++;
            j--;             
        }
 
        return true;
    }
};