Find Duplicate Characters in a String

Solution Steps

  1. Obtain char array from the input String
  2. Loop through the char array, check if the list(List<Character>) already contains the char
    • If No, add the char to the list
    • If Yes, add the char to the duplicates Set<Character>
  3. The elements present in the duplicates Set gives us the required output.

Java Code
package com.java.programs; import java.util.ArrayList; import java.util.List; import java.util.Set; import java.util.TreeSet; public class DuplicateCharacters { public static Set<Character> duplicateCharacters(String input) { List<Character> list = new ArrayList<>(); Set<Character> duplicates = new TreeSet<>(); for (char c : input.toCharArray()) { if (list.contains(c)) { duplicates.add(c); } else { list.add(c); } } return duplicates; } public static void main(String[] args) { System.out.println(duplicateCharacters("aeroplane")); } }
Output
[a, e]

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