Palindrome-Index

What it is

A command-line script that solves the 'Palindrome Index' algorithmic problem. It accepts a series of lowercase strings and determines if they are already palindromes or if removing a single specific character makes them one. It returns the zero-based index of the removable character, or -1 if the string is already a palindrome.

Features

• Detects if a string is already a palindrome
• Identifies the specific index of a character to remove to form a palindrome
• Handles multiple test cases via standard input
• Returns -1 for strings that are already palindromes
• Uses efficient string slicing for substring generation

Quickstart

python palindromeIndex.py

Architecture

flowchart TD
    A[Start] --> B[Read Input Integer T]
    B --> C{Loop T times}
    C -->|Next String S| D[Check isPalindrome(S)]
    D -->|True| E[Print -1]
    D -->|False| F[Find Mismatch Index i]
    F --> G[Test Remove S[i]]
    G -->|Is Palindrome| H[Print i]
    G -->|Not Palindrome| I[Test Remove S[len-1-i]]
    I -->|Is Palindrome| J[Print len-1-i]
    E --> K{More Cases?}
    H --> K
    J --> K
    K -->|Yes| C
    K -->|No| L[End]

How it's built

The solution is implemented in a single Python file (`palindromeIndex.py`). It uses a two-pointer approach implicitly by comparing the string with its reverse. When a mismatch is found at index `i`, it tests two hypotheses: removing the character at `i` from the original string, or removing the corresponding character from the end (index `len(s)-1-i`). It validates these hypotheses by checking if the resulting substrings are palindromes.

How it runs

sequenceDiagram
    participant User
    participant Main as palindromeIndex.py
    participant Logic as palindromeIndex()
    participant Helper as isPalindrome()
    
    User->>Main: Provide Input (T, Strings)
    loop For each string S
        Main->>Logic: palindromeIndex(S)
        Logic->>Helper: isPalindrome(S)
        alt S is Palindrome
            Helper-->>Logic: True (1)
            Logic-->>Main: Return -1
        else S is Not Palindrome
            Helper-->>Logic: False (0)
            Logic->>Logic: Find first mismatch i
            Logic->>Helper: isPalindrome(S without i)
            alt Substring is Palindrome
                Helper-->>Logic: True
                Logic-->>Main: Return i
            else Substring is Not Palindrome
                Helper-->>Logic: False
                Logic->>Helper: isPalindrome(S without mirror i)
                Helper-->>Logic: True
                Logic-->>Main: Return mirror index
            end
        end
        Main->>User: Print Result
    end

How to apply & reuse

This code serves as a reference implementation for string manipulation algorithms, specifically for interview preparation involving palindromes and greedy approaches. It demonstrates basic string slicing, reversal, and iterative comparison logic in Python 2/3 compatible syntax.

At a glance