✨ How to Check if a String is a Palindrome in DSA

🔍 What is a Palindrome?

A palindrome is a string that remains the same when reversed.
Examples:

• "madam" → Palindrome ✅

• "racecar" → Palindrome ✅

• "hello" → Not a Palindrome ❌

This concept is widely used in string manipulation problems, interview coding tests, and pattern-based algorithm challenges.

🧠 Approach to Solve Palindrome Problem

1️⃣ Reverse and Compare

• Reverse the given string.

• Compare it with the original string.

• If both are equal → It’s a palindrome.

🔸 Time Complexity: O(n)
🔸 Space Complexity: O(n) (for storing reversed string)

2️⃣ Two-Pointer Technique (Efficient)

• Place one pointer at the start and one at the end of the string.

• Compare characters at both positions.

• If all characters match till the middle → Palindrome.

• If any mismatch → Not a palindrome.

🔸 Time Complexity: O(n)
🔸 Space Complexity: O(1) (in-place check, more efficient)

💻 Code Implementations

✅ C++ Implementation

#include <iostream>
using namespace std;

bool isPalindrome(string str) {
    int left = 0, right = str.length() - 1;
    while (left < right) {
        if (str[left] != str[right]) {
            return false;
        }
        left++;
        right--;
    }
    return true;
}

int main() {
    string s = "racecar";
    if (isPalindrome(s))
        cout << s << " is a palindrome.";
    else
        cout << s << " is not a palindrome.";
    return 0;
}

✅ Java Implementation

public class PalindromeCheck {
    public static boolean isPalindrome(String str) {
        int left = 0, right = str.length() - 1;
        while (left < right) {
            if (str.charAt(left) != str.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }

    public static void main(String[] args) {
        String s = "madam";
        if (isPalindrome(s))
            System.out.println(s + " is a palindrome.");
        else
            System.out.println(s + " is not a palindrome.");
    }
}

✅ Python Implementation

def is_palindrome(s: str) -> bool:
    return s == s[::-1]

# Test
s = "level"
if is_palindrome(s):
    print(f"{s} is a palindrome.")
else:
    print(f"{s} is not a palindrome.")

🏆 Practical Applications of Palindrome Check

• Data Validation: Checking symmetric patterns in data.

• Cryptography: Palindromes can appear in encoded/decoded strings.

• Interview Questions: Common coding problem for beginners.

• DNA Sequences: Some biological DNA strands form palindrome patterns.

📌 Key Takeaways

• A palindrome reads the same forward and backward.

• Two main approaches: Reverse & Compare (simple) and Two-Pointer (efficient).

• Time Complexity: O(n).

• Frequently asked in DSA interviews and coding challenges.

👉 By mastering this problem, you strengthen your string manipulation skills — a foundation for advanced DSA topics like pattern matching, dynamic programming, and hashing problems.