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Virtual Algorithm Lab

Palindrome Checker

{ }
++ ++
0
0
s[l] == s[r] — Convergence
Palindrome Two-Pointer System
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Palindrome Checker

"racecar" → true · two markers converge inward checking symmetry

The Word, Live
Custom Word:
Step by Step
Step 1 / 9

The Code Behind It
palindrome.py 

    
In plain English: 

  


  
Theory & Fundamentals

  

    
The Two-Pointer Technique

    
A palindrome is a sequence that reads the same forwards and backwards. By using a Left and Right pointer, we check characters from the outside in. If any pair doesn't match, we can immediately exit (return False). This achieves O(1) auxiliary space and O(N) time complexity.

  



  
Knowledge Check

  
  

    
Q1: Tracing the Algorithm

    
If the word is "RADAR", what is the value of s[l] and s[r] on the very first step?

    

      
      
    

    

  


  

    
Q2: Early Exit

    
If we check the word "HELLO", how many pairs of letters do we actually compare before knowing it's not a palindrome?

    
    

  


  

    
Q3: Space Complexity

    
What is the auxiliary space complexity of checking a palindrome using two pointers?