In this post we will learn How to find first non-repeated character in a given String in Java with/without using Java inbuilt API or data structure.
We will look three approaches to solve this problem statement.
- Without using any in-built API or data structure
- Using LinkedHashMap data structure
- using String class indexOf(int ch) and lastIndexOf(int ch) methods
Approach 1:
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package com.kkjavatutorials.client; import java.util.Scanner; /** * @author KK JavaTutorials * This java program is all about how to find first Non repeated character in a given input String */ public class ClientTest1 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out.println("Enter String to find first non-repeated character::"); String inputText = scanner.next(); Character c = findFirstNonRepeatedCharacterFromString(inputText); if(c !=null) System.out.println("First Non Repeated character is: " + c); else System.out.println("There is no single Non Repeated character found"); } catch (Exception e) { e.printStackTrace(); } } private static Character findFirstNonRepeatedCharacterFromString(String inputText) { // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()) { System.out.println("Enter valid input text.."); return null; } boolean isNonRepeatedCharFound = false; for (int i = 0; i < inputText.length(); i++) { isNonRepeatedCharFound = true; char c = inputText.charAt(i); for (int j = 0; j < inputText.length(); j++) { /* * if we find matching character then set the boolean field to * false we also skip the char which is already compared */ if (c == inputText.charAt(j) && i != j) { isNonRepeatedCharFound = false; break; } } if (isNonRepeatedCharFound) { return c; } } if (!isNonRepeatedCharFound) { return null; } return null; } } |
Approach 2:
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package com.kkjavatutorials.client; import java.util.LinkedHashMap; import java.util.Map; import java.util.Scanner; import java.util.Map.Entry; /** * @author KK JavaTutorials * This java program is all about how to find first Non repeated character in a given input String */ public class ClientTest2 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out.println("Enter String to find first non-repeated character::"); String inputText = scanner.next(); Character c = findFirstNonRepeatedCharacterFromString(inputText); if(c != null) System.out.println("First Non Repeated character is: " + c); else System.out.println("There is no single Non Repeated character found"); } catch (Exception e) { e.printStackTrace(); } } private static Character findFirstNonRepeatedCharacterFromString(String inputText) { // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()) { System.out.println("Enter valid input text.."); return null; } //LinkedHashMap always maintains the insertion order that the region to choose this data structure Map<Character, Integer> charCountMap = new LinkedHashMap<Character, Integer>(); for (int i = 0; i < inputText.length(); i++) { Character ch = inputText.charAt(i); // If character found in map increment the count if (charCountMap.containsKey(ch)) { charCountMap.put(ch, charCountMap.get(ch) + 1); } else { //Initialize the count by 1 first time charCountMap.put(ch, 1); } } //Iterate the above map and find the first character with count value 1 for (Entry<Character, Integer> entry : charCountMap.entrySet()) { if (entry.getValue() == 1) { return entry.getKey(); } } return null; } } |
Approach 3:
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package com.kkjavatutorials.client; import java.util.Scanner; /** * @author KK JavaTutorials * This java program is all about how to find first Non repeated character in a given input String */ public class ClientTest3 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out.println("Enter String to find first non-repeated character::"); String inputText = scanner.next(); Character c = findFirstNonRepeatedCharacterFromString(inputText); if(c != null) System.out.println("First Non Repeated character is: " + c); else System.out.println("There is no single Non Repeated character found"); } catch (Exception e) { e.printStackTrace(); } } /* * Here I have used logic- indexOf () method returns the index of the first * occurrence of a specified character where the lastIndexOf () method returns the * index of the last occurrence of the specified character. If both the indexes are equal * it means that character is only once in the input string. */ private static Character findFirstNonRepeatedCharacterFromString(String inputText) { // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()) { System.out.println("Enter valid input text.."); return null; } for (int i = 0; i < inputText.length(); i++) { Character ch = inputText.charAt(i); if (inputText.indexOf(ch) == inputText.lastIndexOf(ch)) { return ch; } } return null; } } |
I have checked all the above programs for few inputs as below. You may check for other input as well
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Enter String to find first non-repeated character:: java First Non Repeated character is: j Enter String to find first non-repeated character:: tutorials First Non Repeated character is: u Enter String to find first non-repeated character:: KKJavaTutorials First Non Repeated character is: J |
That’s all about this topic How to find first non-repeated character in a given String in Java.
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