Valid Palindrome | LeetCode 125 | C++ Solution with Explanation

In this video, we solve LeetCode Problem 125: Valid Palindrome using a clean and efficient approach that is perfect for beginners as well as interview preparation. We start by understanding the problem statement and the key requirement: ignoring all non-alphanumeric characters and treating uppercase and lowercase letters as the same. This adds an extra layer of complexity compared to a normal palindrome check. Then, we walk through detailed examples step by step to see how to filter out unwanted characters and compare the string effectively. Instead of creating a new string, we focus on an optimized two-pointer approach that works directly on the original string. 🧠 What You Will Learn in This Video: What is a palindrome and how to identify it Handling edge cases like spaces and special characters Ignoring case sensitivity in string comparison Step-by-step dry run with examples Two-pointer technique for string problems Clean and optimized C++ implementation Time and Space Complexity analysis 🧩 Problem Summary: You are given a string s. Your task is to determine whether it is a palindrome after: Converting all uppercase letters to lowercase Removing all non-alphanumeric characters Return: true if it is a palindrome false otherwise 💡 Approach Explained: We use a two-pointer technique: Initialize two pointers: One at the beginning One at the end Move both pointers inward: Skip non-alphanumeric characters Convert characters to lowercase Compare characters: If they are not equal → return false Otherwise, continue If all characters match → return true This approach avoids extra space and is highly efficient. ⏱️ Complexity Analysis: Time Complexity: O(n) Space Complexity: O(1) Where n is the length of the string. 💻 Topics Covered: Strings Two-pointer technique Character handling String manipulation 🚀 Why Watch This Video? This is one of the most commonly asked string problems in coding interviews. It helps you master: string traversal filtering characters efficient comparison techniques A must-know problem for anyone preparing for technical interviews. #LeetCode125 #DSA #CodingForBeginners #LeetCodeEasy #Strings #TwoPointers #ProblemSolving #CodingInterview #LearnToCode #Cpp #Algorithms