Question 6 : Find first non repeated character in String in java?

Solution: There are many ways to find it.

Some of them are:

• Using  LinkedHashMap.
• Using indexOf and lastIndexOf methods.

One of the interview questions is “How will you find the first nonrepeating character in String.”

For example:

• If the input string is “analogy”,  then the program should return ‘n’
• If the input string is “easiest”, then the program should return ‘a’

First approach:

We will use LinkedHashMap to find the first nonrepeating character in String.

Algorithm:

• Get character while looping over String
• Put this character in LinkedHashMap with a count. If a character is already there, increase the count by 1.
• Get count from LinkedHashMap while iterating. If the count is 1, return that character as LinkedHashMap maintains insertion order.

Program::

package org.cloudTechtwitter;
 
import java.text.*;
import java.util.*;
import java.util.Map.Entry;
 
public class GetFirstNonRepeatingCharacterMain {
 public static void main(String[] args) {
  System.out
    .println("First non repeated character for String analogy is : "
      + getNonRepeatedCharacter("analogy"));
  System.out
    .println("First non repeated character for String easiest is : "
      + getNonRepeatedCharacter("easiest"));
 }
 
 public static Character getNonRepeatedCharacter(String str) {
  Map<Character, Integer> countCharacters = new LinkedHashMap<Character, Integer>();
  for (int i = 0; i < str.length() - 1; i++) {
   Character c = str.charAt(i);
   if (!countCharacters.containsKey(c)) {
    countCharacters.put(c, 1);
   } else {
    countCharacters.put(c, countCharacters.get(c) + 1);
   }
  }
  // As LinkedHashMap maintains insertion order, first character with
  // count 1 should return first non repeated character
  for (Entry<Character, Integer> e : countCharacters.entrySet()) {
   if (e.getValue() == 1)
    return e.getKey();
 
  }
  return null;
 
 }
}

When you run above program, you will get following output
First non repeated character for String analogy is : n

First non repeated character for String easiest is : a

Second Approach:

Algorithm:

• Iterate through each character of string.
• If lastIndexOf and indexOf return same value, then it is first non repeating character in the String.

Program::

package org.cloudTechtwitter;

public class GetFirstNonRepeatingCharacterMain
{
 public static void main(String[] args)
 {
        System.out.println("First non repeated character for String analogy is : "+getNonRepeatedCharacter("analogy"));
        System.out.println("First non repeated character for String easiest is : "+getNonRepeatedCharacter("easiest"));
 }
 public static Character getNonRepeatedCharacter(String str)
 {     char charaaray[]=str.toCharArray();
       for (int i=0; i<str.length();i++)
      {
          if (str.lastIndexOf(charaaray[i]) == str.indexOf(charaaray[i]))
               return charaaray[i];
      }
  return null;
 }
}

When you run the above program, you will get the following output:

First non repeated character for String analogy is : n
First non repeated character for String easiest is : a

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