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In this post, we will look at a Core Java program to find the longest sub-string in a String without repeated chars.
Here is the program:
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package com.clearurdoubt; import java.util.Scanner; /** * * @author clearurdoubt * */ public class FindSubstring { public static void main(String[] args) { System.out.println("Please enter an input string:"); // request user to provide an empty string Scanner in = new Scanner(System.in); // Scanner instance to read the input from console String input = in.nextLine().trim(); // Read the input and trim the spaces around it // Find and print the longest substring. System.out.println("The longest substring in the input \"" + input + "\" is \"" + findLongestSubstring(input) + "\""); in.close(); } /** * Method to find the longest substring without repeated characters * @param input string from user * @return */ private static String findLongestSubstring(String input) { String longest = ""; // Variable for storing the longest substring // Loop through the characters from starting to ending for(int i=0; i < input.length() - 1; i++) { String substr = ""; // Local variable to find the current substring without repeated chars // Loop through characters from index "i" till the end of input for(int j = i; j < input.length() - 1; j++) { char ch = input.charAt(j); // Current character if(substr.indexOf(ch) == -1) // If substr doesn't contain the current character { substr += ch; // Time to append the current char to substr } else { break; // Current char already in the substr, so break out the inner loop } } // Time to check if the local substr is longer than "longest" variable if(longest.length() < substr.length()) { longest = substr; } } return longest; // Return the longest substring } } |
Output:
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