Job Updates
Interviews
Connect
Connect & get Notified

Program to Find the Non-repeating character in a String

Program to check : Non-Repeating Character in a String

Definition & Explanation

The task is to find non-repeating characters in a given string, i.e., characters that occur only once in the string.

More Description

Program Logic

  1. Create a dictionary (or hash map) to store the frequency/count of each character in the string.
  2. Iterate through each character in the string and update its count in the dictionary.
  3. Iterate through the string again and check if the count of each character is 1. If so, it means the character is non-repeating, so add it to a result string.
  4. Finally, return the result string containing all non-repeating characters.
C

Method 1 :

#include <stdio.h>
#include <string.h>

#define MAX_CHAR 256

void findNonRepeatingChars(char* str) {
    int count[MAX_CHAR] = {0};

    // Count frequency of each character
    for (int i = 0; str[i]; i++)
        count[str[i]]++;

    // Print non-repeating characters
    printf("Non-repeating characters: ");
    for (int i = 0; i < MAX_CHAR; i++) {
        if (count[i] == 1)
            printf("%c ", i);
    }
    printf("\n");
}

int main() {
    char str[] = "hello";
    findNonRepeatingChars(str);
    return 0;
}

Output :

C++

Method 1 :

#include <iostream>
#include <unordered_map>
using namespace std;

void findNonRepeatingChars(string str) {
    unordered_map<char, int> freq;

    // Count frequency of each character
    for (char ch : str)
        freq[ch]++;

    // Print non-repeating characters
    cout << "Non-repeating characters: ";
    for (char ch : str) {
        if (freq[ch] == 1)
            cout << ch << " ";
    }
    cout << endl;
}

int main() {
    string str = "hello";
    findNonRepeatingChars(str);
    return 0;
}

Output :

JAVA

Method 1 :

import java.util.HashMap;
import java.util.Map;

public class NonRepeatingChars {
    public static void findNonRepeatingChars(String str) {
        Map<Character, Integer> freq = new HashMap<>();

        // Count frequency of each character
        for (char ch : str.toCharArray())
            freq.put(ch, freq.getOrDefault(ch, 0) + 1);

        // Print non-repeating characters
        System.out.print("Non-repeating characters: ");
        for (char ch : str.toCharArray()) {
            if (freq.get(ch) == 1)
                System.out.print(ch + " ");
        }
        System.out.println();
    }

    public static void main(String[] args) {
        String str = "hello";
        findNonRepeatingChars(str);
    }
}

Output :

Python

Method 1 :

def find_non_repeating_chars(s):
    freq = {}

    # Count frequency of each character
    for char in s:
        freq[char] = freq.get(char, 0) + 1

    # Print non-repeating characters
    print("Non-repeating characters:", end=" ")
    for char in s:
        if freq[char] == 1:
            print(char, end=" ")
    print()

# Test the function
s = "hello"
find_non_repeating_chars(s)

Output :

Non-repeating characters: h e o
View All Codes