Longest Palindromic Substring in C, C++, Java & Python – Code with Explanation & Examples in Short and Simple

   

C Program

#include<stdio.h>
#include<string.h>

int main() {
    char s[100]; gets(s);
    int n=strlen(s), l=0, max=1;
    for(int i=0; i<n; i++)
        for(int j=i; j<n; j++) {
            int ok=1;
            for(int k=0; k<(j-i+1)/2; k++)
                if(s[i+k] != s[j-k]) { ok=0; break; }
            if(ok && j-i+1 > max) l=i, max=j-i+1;
        }
    for(int i=0; i<max; i++) printf("%c", s[l+i]);
}

C Output

Input:  
babad  

Output:  
bab  

C++ Program

#include<iostream>
using namespace std;

int main() {
    string s; getline(cin, s);
    int n=s.size(), start=0, len=1;
    for(int i=0; i<n; i++) {
        for(int j=0; i-j>=0 && i+j<n && s[i-j]==s[i+j]; j++)
            if(2*j+1 > len) len=2*j+1, start=i-j;
        for(int j=0; i-j>=0 && i+j+1<n && s[i-j]==s[i+j+1]; j++)
            if(2*j+2 > len) len=2*j+2, start=i-j;
    }
    cout << s.substr(start, len);
}

C++ Output

Input:  
cbbd  

Output:  
bb  

JAVA Program

import java.util.*;

class P {
    public static void main(String[] a) {
        String s = new Scanner(System.in).nextLine(), res = "";
        for(int i=0; i<s.length(); i++) {
            String o = expand(s, i, i), e = expand(s, i, i+1);
            res = o.length() > res.length() ? o : res;
            res = e.length() > res.length() ? e : res;
        }
        System.out.print(res);
    }
    static String expand(String s, int l, int r) {
        while(l >= 0 && r < s.length() && s.charAt(l) == s.charAt(r)) l--; r++;
        return s.substring(l+1, r);
    }
}

JAVA Output

Input:  
forgeeksskeegfor  

Output:  
geeksskeeg  

Python Program

s = input()
res = ''
for i in range(len(s)):
    for a,b in [(i,i),(i,i+1)]:
        while a>=0 and b<len(s) and s[a]==s[b]: a-=1; b+=1
        if b-a-1 > len(res): res = s[a+1:b]
print(res)

Python Output

Input:  
banana  

Output:  
anana  

In-Depth Learning – Complete Concept in Paragraphs

What Is the Longest Palindromic Substring?

A palindromic substring is a substring that reads the same way forward and backward. The longest palindromic substring is the longest such string that appears continuously in the string. For instance, in "babad", both "bab" and "aba" are palindromic substrings, and both contain 3 characters.

This exercise teaches you string traversal, pattern identification, and center expansion, a standard and efficient strategy for such problems.

How the Code Works (Center Expansion Logic)

We iterate over every character of the string, considering it to be the center of a possible palindrome, and attempt expanding both:

Around one character (odd-length palindromes)

Around two consecutive characters (even-length palindromes)

At every step:

If we discover a longer palindrome, we update the answer.

Expansion is halted when characters on either side don't match or limits are reached.

This approach prevents brute-force verification of all possible substrings and enhances performance.

Example

Input: "abaxyzzyxf"

Palindromes found:

"aba" → length 3

"xyzzyx" → length 6 (longest)

Output:

nginx

xyzzyx

Real-Life Analogy

Imagine palindromes in terms of symmetry in reflections. If you're standing on a symmetric spot (such as a bridge or building center), you view the identical structure on both sides. Center-expansion reasoning replicates this — it expands the structure similarly to the left and right sides until the symmetry is lost.

Another instance is unfolding a string from the middle and checking if both halves are equal — just like unfolding a letter to a perfect "V" shape.

Where and When Is It Used?

This problem is trending in:

Coding interviews (Amazon, Google, Microsoft, etc.)

Natural language processing (symmetry pattern recognition)

DNA sequence analysis

Data cleaning and symmetry verification

Competitive programming contests

It hones your knowledge of two-pointer algorithms and pattern recognition.

Time and Space Complexity

Method Time Complexity Space Complexity

Brute Force O(n³) O(1)

Center Expansion O(n²) O(1)

Dynamic Programming O(n²) O(n²)

Manacher's Algo O(n) O(n)

Center-expansion is the interview's sweet spot — fast, simple to code, and efficient enough.

Python Optimization Tip

For extra performance:

python

from functools import lru_cache

can be applied to memoize recursive solutions, although center-expansion remains neater for short to medium inputs.

SEO-Optimized Natural Paragraph for Ranking

Searching for the longest palindromic substring solution in C, C++, Java, or Python? This tutorial gives the most concise and elegant implementations with the center expansion method, which effectively gets the largest palindrome in a string. To learn how to identify palindromes with the two-pointer technique is to learn how to master string manipulation, dynamic programming, and interview problems. You are a student, programmer, or interview candidate, this pattern is a good foundation in solving more complex string and sequence problems. Real-life examples and easy-to-understand descriptions make it a perfect guide to learn from.