Java Program to Implement Manacher Algorithm

This is a Java Program to Implement Manacher Algorithm. Manacher algorithm is used to find largest palindromic substring in a given string efficiently.

Here is the source code of the Java Program to Implement Manacher Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

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/**
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 ** Java Program to implement Manacher Algorithm

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 **/
```
```
 
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import java.io.BufferedReader;
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import java.io.InputStreamReader;
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import java.io.IOException;
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/** Class Manacher **/
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public class Manacher
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{
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    /** function to preprocess string **/

    public String preProcess(String str)

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    {
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        int len = str.length();
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        if (len == 0) 
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            return "^$";
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        String s = "^";
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        for (int i = 0; i < len; i++)
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            s += "#" + str.charAt(i);

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        s += "#$";
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        return s;
```
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    }
```

    /** function to get largest palindromic substring **/

    public String getLongestPalindrome(String str)

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    {
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        /** preprocess string **/
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        char[] s = preProcess(str).toCharArray();

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        int N = s.length;
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        int[] p = new int[N + 1];
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        int id = 0, mx = 0;
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        for (int i = 1; i < N - 1; i++)

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        {
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             p[i] = mx > i ? Math.min(p[2 * id - i], mx - i) : 0;

             while (s[i + 1 + p[i]] == s[i - 1 - p[i]])

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                 p[i]++;
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             if (i + p[i] > mx) 
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             {
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                 mx = i + p[i];
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                 id = i;
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             }
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        }
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        /** length of largest palindrome **/

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        int maxLen = 0;
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        /** position of center of largest palindrome **/

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        int centerIndex = 0;
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        for (int i = 1; i < N - 1; i++)

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        {
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            if (p[i] > maxLen) 
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            {
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                maxLen = p[i];
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                centerIndex = i;
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            }
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        }
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        /** starting index of palindrome **/

        int pos = (centerIndex - 1 - maxLen)/2;

        return str.substring(pos , pos + maxLen);

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    }
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    /** Main Function **/
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    public static void main(String[] args) throws IOException

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    {    
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        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        System.out.println("Manacher Algorithm Test\n");

        System.out.println("\nEnter String");

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        String text = br.readLine();
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        Manacher m = new Manacher(); 
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        String longestPalindrome = m.getLongestPalindrome(text);

        System.out.println("\nLongest Palindrome : "+ longestPalindrome);

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    }    
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}
```

Manacher Algorithm Test
 
 
Enter String
civicradarrevivermalayalammadamnoon
 
Longest Palindrome : malayalam

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