Approach : One Liner Java 8 Solution

The similar problem can be solved in Java 8 stream API using one-liner solution as follows –

Java

/*package whatever //do not write package name here */
 
import java.io.*;
import java.util.LinkedHashMap;
import java.util.function.Function;
import java.util.stream.Collectors;
 
class GFG {
   
    private static char findFirstNonRepeatingCharacter(String s) {
        return s.chars()
                .mapToObj(x -> Character.toLowerCase((char) x))
                .collect(Collectors.groupingBy(Function.identity(), 
                                               LinkedHashMap::new, Collectors.counting()))
                .entrySet()
                .stream()
                .filter(x -> x.getValue() == 1)
                .findFirst()
                .orElseThrow()
                .getKey();
    }
   
    public static void main (String[] args) {
        System.out.println(findFirstNonRepeatingCharacter("w3wiki"));
    }
}

Time Complexity : O(n)

Space Complexity : O(n) //As internally it is using a new Map to store data

Related Problem: K’th Non-repeating Character

Find first non-repeating character of given String

Given a string S consisting of lowercase Latin Letters, the task is to find the first non-repeating character in S.

Examples:

Input: “w3wiki”
Output: f
Explanation: As ‘f’ is first character in the string which does not repeat.

Input: “algorithm”
Output: a
Explanation: As ‘a’ is first character in the string which does not repeat.

Naive Approach:

The idea is to loop over the string and for every character check the occurrence of the same character in the string. If the count of its occurrence is 1 then return that character. Otherwise, search for the remaining characters.

Note: In python to find the occurrence of a character in the string there is an In-Built Function string.count().

Below is the implementation of the above approach:

C++

#include <bits/stdc++.h>
using namespace std;
 
int main()
{
    string string = "w3wikifor";
    int index = -1;
    char fnc = ' ';
      
    if(string.size()==0){
      cout<<"EMPTY STRING"<<endl;
    }
   
    for (auto i : string) {
        if (count(string.begin(), string.end(), i) == 1) {
            fnc = i;
            break;
        }
        else {
            index += 1;
        }
    }
    if (index == string.size()-1) {
        cout << "All characters are repeating" << endl;
    }
    else {
        cout << "First non-repeating character is " << fnc
             << endl;
    }
    return 0;
}
 
// This code is contributed by aakansharao1111

Java

//Java code for the above approach
 
import java.io.*;
 
public class GFG {
    public static void main(String[] args) {
        String string = "w3wiki";
        int index = -1;
        char fnc = ' ';
       
       if(string.length()==0){
         System.out.println("EMPTY STRING");
       }
       
        for (char i : string.toCharArray()) {
            if (string.indexOf(i) == string.lastIndexOf(i)) {
                fnc = i;
                break;
            }
            else {
                index += 1;
            }
        }
        if (index == string.length()-1) {
            System.out.println("All characters are repeating");
        }
        else {
            System.out.println("First non-repeating character is " + fnc);
        }
    }
}
 
// This code is contributed by aakansharao1111

Python3

# Python program to print the first non-repeating character
 
string = "w3wiki"
index = -1
fnc = ""
 
if len(string) == 0 :
  print("EMTPY STRING");
 
for i in string:
    if string.count(i) == 1:
        fnc += i
        break
    else:
        index += 1
if index == len(string)-1 :
    print("All characters are repeating ")
else:
    print("First non-repeating character is", fnc)
 
#// This code is contributed by aakansharao1111

C#

// C# implementation of the above approach
 
using System;
using System.Collections.Generic;
using System.Linq;
 
class Gfg
{
    public static void Main(string[] args)
    {
        string str = "w3wiki";
        int index = -1;
        char fnc = ' ';
         
        if(str.Length == 0){
          Console.WriteLine ("EMPTY STRING");
        }
       
        foreach (char i in str)
        {
            if(str.Count(t => t == i)==1){
                fnc = i;
                break;
            }
            else {
                index += 1;
            }
        }
        if (index == str.Length-1) {
            Console.WriteLine("All characters are repeating ");
        }
        else {
            Console.WriteLine("First non-repeating character is " + fnc);
        }
    }
}
 
// This code is contributed by aakansharao1111

Javascript

const string = "w3wiki";
let index = -1;
let fnc = ' ';
 
if(string.length == 0){
console.log("EMPTY STRING");
}
 
for (let i of string) {
    if (string.split(i).length - 1 === 1) {
        fnc = i;
        break;
    } else {
        index += 1;
    }
}
if (index === string.length-1) {
    console.log("All characters are repeating.");
} else {
    console.log(`First non-repeating character is ${fnc}`);
}
 
// This code is contributed by aakansharao1111

Output

All characters are repeating

Time Complexity: O(N²), Traverse over the string for every character in the string of size N.
Auxiliary Space: O(1)

Approach : One Liner Java 8 Solution

Java

Time Complexity : O(n)

Space Complexity : O(n) //As internally it is using a new Map to store data

Find first non-repeating character of given String

C++

Java

Python3

C#

Javascript

Categories

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Approach : One Liner Java 8 Solution

Java

Time Complexity : O(n)

Space Complexity : O(n) //As internally it is using a new Map to store data

Find first non-repeating character of given String

C++

Java

Python3

C#

Javascript

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Contact US