Find all distinct palindromic sub-strings of a given string - Java Algorithm

Java examples for Algorithm:String

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Description

Find all distinct palindromic sub-strings of a given string

Demo Code


import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;


public class ManacherAlgorithim {
  public String preProcess(String str) {
    int len = str.length();
    if (len == 0)
      return "^$";
    String s = "^";
    for (int i = 0; i < len; i++)
      s += "#" + str.charAt(i);
    s += "#$";//from w  ww  .j  av a 2  s .  co m
    return s;
  }

  /** function to get largest palindromic substring **/
  public String getLongestPalindrome(String str) {
    char[] s = preProcess(str).toCharArray();
    int N = s.length;
    int[] p = new int[N + 1];
    int id = 0, mx = 0;
    for (int i = 1; i < N - 1; i++) {
      p[i] = mx > i ? Math.min(p[2 * id - i], mx - i) : 0;
      while (s[i + 1 + p[i]] == s[i - 1 - p[i]])
        p[i]++;
      if (i + p[i] > mx) {
        mx = i + p[i];
        id = i;
      }
    }

    /** length of largest palindrome **/
    int maxLen = 0;
    /** position of center of largest palindrome **/
    int centerIndex = 0;
    for (int i = 1; i < N - 1; i++) {

      if (p[i] > maxLen) {
        maxLen = p[i];
        centerIndex = i;
      }
    }
    /** starting index of palindrome **/
    // generate all possible string which form palindrom
    int pos = (centerIndex - 1 - maxLen) / 2;

    for (int j = 1; j < N - 1; j++) {
      int localLen = p[j];
      int localIndex = j;
      int localPos = (localIndex - 1 - localLen) / 2;

      if (p[j] > 1) {

        String other = str.substring(localPos, localPos + localLen);

        System.out.println("OTHER PRESENT ARE:" + other);
      }
    }
    return str.substring(pos, pos + maxLen);

  }

  /** Main Function **/
  public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    System.out.println("Manacher Algorithm Test\n");
    System.out.println("\nEnter String");
    String text = br.readLine();

    ManacherAlgorithim m = new ManacherAlgorithim();
    String longestPalindrome = m.getLongestPalindrome(text);
    System.out.println("\nLongest Palindrome : " + longestPalindrome);
  }
}

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