Six months ago, I thought I knew palindromes.
I'd write this confident one-liner:
pythonreturn s == s[::-1]
Pat myself on the back for being "Pythonic," and move on.
Then I started grinding LeetCode. Problem 9. Palindrome Number.
"Easy," I thought. "Just convert to string and—"
Constraint: Solve it without converting the integer to a string.
Wait, what?
That's when I realized: I didn't understand palindromes. I just memorized a trick.
The Wake-Up Call
After 50+ palindrome variations on LeetCode, I discovered something uncomfortable: the problems aren't about palindromes at all.
They're about:
- Understanding space-time tradeoffs
- Recognizing when to optimize
- Adapting algorithms to constraints
- Thinking beyond the obvious solution
Every palindrome problem is actually teaching you how to think like a systems engineer.
Let me show you what I learned.
The Five Methods That Actually Matter
Method 1: The Slice Trick (And Why It's Not Always Wrong)
Everyone says s[::-1] is "bad" because it uses O(n) space.
But here's what nobody tells you: In CPython, it's 40x faster than manual loops for large strings because it's implemented in C.
I benchmarked a million-character string:
- Slicing: ~0.15 seconds
- Manual loop: ~6.2 seconds
The lesson? "Best practice" depends on context. If you're processing user input (strings under 10,000 chars), the slice method is perfectly fine. If you're parsing genomic sequences? Different story.
When an interviewer asks you to optimize, you need to know why you're optimizing and what you're trading off.
Method 2: Two Pointers (The Interview Answer Everyone Expects)
This is the solution interviewers want to see:
def is_palindrome(s):
left, right = 0, len(s) - 1
while left < right:
if s[left] != s[right]:
return False
left += 1
right -= 1
return True
Why interviewers love it:
- Shows you understand O(1) space optimization
- Demonstrates algorithmic thinking
- Proves you can work with pointers/indices
But here's the trap: If you jump straight to this without acknowledging the simpler solution, you look like you're just reciting memorized patterns.
Pro move: Start with slicing, then say: "If we need O(1) space, I'd use two pointers..." This shows you understand the tradeoff.
(https://emitechlogic.com/how-to-check-palindrome-in-python/)
Method 3: Recursion (The One You Shouldn't Use in Production)
I spent way too long trying to make recursive palindrome checking "elegant."
def is_palindrome(s):
if len(s) <= 1:
return True
return s[0] == s[-1] and is_palindrome(s[1:-1])
It feels smart. It looks clean.
It's also terrible.
- Stack overflow on long strings
- Slower than iterative
- Creates n substring copies
When to use it: Never in production. Only in interviews when explicitly asked to demonstrate recursion understanding, or when teaching recursion concepts.
The real lesson: Just because you can make something recursive doesn't mean you should.
Method 4: Pure Math (No Strings Allowed)
This one broke my brain at first.
LeetCode 9: "Determine whether an integer is a palindrome without converting it to a string."
My first reaction: "That's... impossible?"
But it's not. You can reverse a number mathematically:
def is_palindrome(num):
if num < 0:
return False
original = num
reversed_num = 0
while num > 0:
digit = num % 10
reversed_num = reversed_num * 10 + digit
num //= 10
return original == reversed_num
Key insight: num % 10 extracts the last digit. num // 10 removes it. Build the reversed number digit by digit.
This works because: 121 → extract 1 → 12 → extract 2 → 1 → extract 1
Reverse build: 0 → 1 → 12 → 121
Why it matters: Shows you can think beyond obvious approaches. Teaches modular arithmetic. Demonstrates O(1) space with O(log n) time.
Method 5: Valid Palindrome (The Real-World Version)
Most tutorials stop at basic palindromes.
Then you see LeetCode 125: "A man, a plan, a canal: Panama" should return True.
Wait, that's not a palindrome... or is it?
A man, a plan, a canal: Panama
↓ (remove non-alphanumeric, lowercase)
amanaplanacanalpanama
↓ (check)
✓ Palindrome!
This is where it gets practical. Real-world strings have:
- Spaces
- Punctuation
- Mixed case
- Special characters
You need to clean the string first or skip non-alphanumeric characters on the fly.
Two approaches:
Approach 1: Clean first, then check (uses O(n) space)
Approach 2: Two pointers that skip invalid chars (uses O(1) space)
The interview moment: When you instinctively reach for Approach 1 (simpler), then pause and say "Actually, if memory is a concern, I can do this with two pointers..."
That's the sign of someone who thinks about constraints.
The Pattern I Wish I'd Seen Earlier
After 50+ problems, I noticed this pattern:
Easy problems → Test if you know the basic algorithm
Medium problems → Add constraints (space/time limits)
Hard problems → Combine multiple concepts (palindrome + linked list, palindrome with one deletion allowed)
Each method I learned wasn't just "another way to solve palindromes."
It was teaching me:
- Slicing → Language features vs manual implementation
- Two-pointer → Space optimization techniques
- Recursion → When elegance costs too much
- Math approach → Thinking outside the data structure
- Valid palindrome → Handling real-world messiness
What Actually Matters in Interviews
Here's what I learned after fumbling through practice interviews:
Don't just solve the problem. Narrate your thinking.
Bad answer:
types code silently
"Here's the solution."
Good answer:
"I'll start with the straightforward slicing approach. This is O(n) space because we're creating a reversed copy. If that's a concern, I can optimize to O(1) space using two pointers. Which would you prefer?"
You're not being tested on finding the perfect solution immediately.
You're being tested on:
- Do you understand tradeoffs?
- Can you recognize when to optimize?
- Do you write working code first, then improve it?
- Can you communicate your thought process?
The Resources That Actually Helped
After wasting time on random tutorials, these actually moved the needle:
For Complete Code Examples and Interactive Visualizations
I wrote a detailed guide with all 5 methods, complexity analysis, and visual explanations:
(https://emitechlogic.com/how-to-check-palindrome-in-python/)
For All the Code in One Place
I put together a GitHub repo with every method, edge cases, and test cases:
(github: https://github.com/Emmimal/how-to-check-palindrome-in-python)
For Practice Problems
LeetCode 9: Palindrome Number
LeetCode 125: Valid Palindrome
LeetCode 680: Valid Palindrome II (delete one char)
LeetCode 234: Palindrome Linked List
Start with 9 and 125. They teach 80% of what you need.
The Mistake I See Everywhere
Beginners learn s == s[::-1] and think they're done.
Intermediate devs learn two-pointers and think slicing is "wrong."
Both are missing the point.
The goal isn't to memorize the "best" solution. It's to understand when each approach makes sense.
- Writing a quick script? Slice away.
- Processing gigabytes of data? Two pointers.
- Interview explicitly asks for recursion? Show it, then mention why iterative is better.
- Numbers only? Pure math.
- Real-world strings? Valid palindrome.
The skill isn't knowing all five methods. It's knowing which one to reach for.
What I Wish Someone Told Me Six Months Ago
If you're just starting:
- Learn the slice method first. Write working code.
- Learn two-pointers second. Understand why it's "better" (and when it's not).
- Try the recursive version once. Then never use it in production.
- Tackle LeetCode 9 to understand the math approach.
- Master valid palindrome (LeetCode 125) because that's the real-world version.
Don't try to memorize all five at once. Build them up one at a time.
And remember: Interviews aren't about knowing the optimal solution instantly. They're about showing you can think through problems systematically.
Your Turn
Which method surprised you the most?
Have you been hit with a palindrome problem in an interview? What was the twist they added?
Drop your experience in the comments. Let's help each other level up.
ResourcesFull Guide with Interactive Visualizations:
How to Check Palindrome in Python: 5 Efficient Methods (2026 Guide)(https://emitechlogic.com/how-to-check-palindrome-in-python/)
Complete Code Repository:
GitHub - Palindrome Methods in Python(https://github.com/Emmimal/how-to-check-palindrome-in-python)
Practice Problems:
LeetCode 9: Palindrome Number
LeetCode 125: Valid Palindrome
LeetCode 680: Valid Palindrome II
LeetCode 234: Palindrome Linked List
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