# K’th Non-repeating Character

Last Updated : 13 May, 2024

Given a string str of length n (1 <= n <= 106) and a number k, the task is to find the kth non-repeating character in the string.

Examples:

Input : str = geeksforgeeks, k = 3
Output : r
Explanation: First non-repeating character is f, second is o and third is r.

Input : str = geeksforgeeks, k = 2
Output : o

Input : str = geeksforgeeks, k = 4
Output : Less than k non-repeating characters in input.

This problem is mainly an extension of the First non-repeating character problem.

## K’th Non-repeating Character using Nested Loop:

A Simple Solution is to run two loops. Start traversing from the left side. For every character, check if it repeats or not. If the character doesn’t repeat, increment the count of non-repeating characters. When the count becomes k, return the character.

Below is the implementation of the above idea:

C++ ```// Include all standard libraries #include <bits/stdc++.h> using namespace std; // Define a function to find the kth non-repeating character // in a string char kthNonRepeatingChar(string str, int k) { // Initialize count and result variables to 0 and null // character, respectively int count = 0; char result = '\0'; // Loop through each character in the string for (int i = 0; i < str.length(); i++) { // Assume that the current character does not repeat bool repeating = false; // Loop through the rest of the string to check if // the current character repeats for (int j = 0; j < i; j++) { if(str[j]==str[i]) { repeating = true; } } for (int j = i + 1; j < str.length(); j++) { if (str[i] == str[j]) { // If the current character repeats, set the // repeating flag to true and exit the loop repeating = true; } } // If the current character does not repeat, // increment the count of non-repeating characters if (!repeating) { count++; // If the count of non-repeating characters // equals k, set the result variable to the // current character and exit the loop if (count == k) { result = str[i]; break; } } } // Return the result variable return result; } // Define the main function to test the kthNonRepeatingChar // function int main() { // Define an example string and value of k string str = "geeksforgeeks"; int k = 3; // Call the kthNonRepeatingChar function with the // example string and value of k char result = kthNonRepeatingChar(str, k); // Check if the result variable contains a non-null // character and print the appropriate message if (result == '\0') { cout << "There is no kth non-repeating character " "in the string.\n"; } else { cout << "The " << k << "th non-repeating character in the string " "is " << result << ".\n"; } // End the program return 0; } ``` Java ```// Import required libraries import java.util.*; // Define a class to find the kth non-repeating character // in a string public class Main { public static char kthNonRepeatingChar(String str, int k) { // Initialize count and result variables to 0 and // null character, respectively int count = 0; char result = '\0'; // Loop through each character in the string for (int i = 0; i < str.length(); i++) { // Assume that the current character does not // repeat boolean repeating = false; // Loop through the rest of the string to check // if the current character repeats for (int j = i + 1; j < str.length(); j++) { if (str.charAt(i) == str.charAt(j)) { // If the current character repeats, set // the repeating flag to true and exit // the loop repeating = true; break; } } // If the current character does not repeat, // increment the count of non-repeating // characters if (!repeating) { count++; // If the count of non-repeating characters // equals k, set the result variable to the // current character and exit the loop if (count == k) { result = str.charAt(i); break; } } } // Return the result variable return result; } // Define the main function to test the // kthNonRepeatingChar function public static void main(String[] args) { // Define an example string and value of k String str = "geeksforgeeks"; int k = 3; // Call the kthNonRepeatingChar function with the // example string and value of k char result = kthNonRepeatingChar(str, k); // Check if the result variable contains a non-null // character and print the appropriate message if (result == '\0') { System.out.println( "There is no kth non-repeating character " + "in the string."); } else { System.out.println( "The " + k + "th non-repeating character in the string " + "is " + result + "."); } } } ``` Python ```# Define a function to find the kth non-repeating character # in a string def kthNonRepeatingChar(s: str, k: int) -> str: # Initialize count and result variables to 0 and null # character, respectively count = 0 result = '\0' # Loop through each character in the string for i in range(len(s)): # Assume that the current character does not repeat repeating = False # Loop through the rest of the string to check if # the current character repeats for j in range(i + 1, len(s)): if s[i] == s[j]: # If the current character repeats, set the # repeating flag to true and exit the loop repeating = True break # If the current character does not repeat, # increment the count of non-repeating characters if not repeating: count += 1 # If the count of non-repeating characters # equals k, set the result variable to the # current character and exit the loop if count == k: result = s[i] break # Return the result variable return result # Define the main function to test the kthNonRepeatingChar # function if __name__ == '__main__': # Define an example string and value of k s = "geeksforgeeks" k = 3 # Call the kthNonRepeatingChar function with the # example string and value of k result = kthNonRepeatingChar(s, k) # Check if the result variable contains a non-null # character and print the appropriate message if result == '\0': print("There is no kth non-repeating character " "in the string.") else: print(f"The {k}th non-repeating character in the string " f"is {result}.") # This code is contributed by Susobhan Akhuli ``` C# ```using System; public class Program { // Define a function to find the kth non-repeating // character in a string static char kthNonRepeatingChar(string str, int k) { // Initialize count and result variables to 0 and // null character, respectively int count = 0; char result = '\0'; // Loop through each character in the string for (int i = 0; i < str.Length; i++) { // Assume that the current character does not // repeat bool repeating = false; // Loop through the rest of the string to check // if the current character repeats for (int j = i + 1; j < str.Length; j++) { if (str[i] == str[j]) { // If the current character repeats, set // the repeating flag to true and exit // the loop repeating = true; break; } } // If the current character does not repeat, // increment the count of non-repeating // characters if (!repeating) { count++; // If the count of non-repeating characters // equals k, set the result variable to the // current character and exit the loop if (count == k) { result = str[i]; break; } } } // Return the result variable return result; } // Define the main function to test the // kthNonRepeatingChar function static void Main(string[] args) { // Define an example string and value of k string str = "geeksforgeeks"; int k = 3; // Call the kthNonRepeatingChar function with the // example string and value of k char result = kthNonRepeatingChar(str, k); // Check if the result variable contains a non-null // character and print the appropriate message if (result == '\0') { Console.WriteLine( "There is no kth non-repeating character " + "in the string."); } else { Console.WriteLine( "The " + k + "th non-repeating character in the string is " + result + "."); } } } // This code is contributed by Susobhan Akhuli ``` JavaScript ```// Define a function to find the kth non-repeating character // in a string function kthNonRepeatingChar(str, k) { // Initialize count and result variables to 0 and null // character, respectively let count = 0; let result = "\0"; // Loop through each character in the string for (let i = 0; i < str.length; i++) { // Assume that the current character does not repeat let repeating = false; // Loop through the rest of the string to check if // the current character repeats for (let j = i + 1; j < str.length; j++) { if (str[i] == str[j]) { // If the current character repeats, set the // repeating flag to true and exit the loop repeating = true; break; } } // If the current character does not repeat, // increment the count of non-repeating characters if (!repeating) { count++; // If the count of non-repeating characters // equals k, set the result variable to the // current character and exit the loop if (count == k) { result = str[i]; break; } } } // Return the result variable return result; } // Define the main function to test the kthNonRepeatingChar // function // Define an example string and value of k let str = "geeksforgeeks"; let k = 3; // Call the kthNonRepeatingChar function with the // example string and value of k let result = kthNonRepeatingChar(str, k); // Check if the result variable contains a non-null // character and print the appropriate message if (result == "\0") { console.log("There is no kth non-repeating character in the string."); } else { console.log(`The \${k}th non-repeating character in the string is \${result}`); } ```

Output
```The 3th non-repeating character in the string is r.

```

Time Complexity: O(nÂ²)
Auxiliary Space: O(1)

## K’th Non-repeating Character using Hashing:

• Create an empty hash map to store character counts.
• Loop through the string and update the counts of each character in the hash map.
• Loop through the string again and find the kth non-repeating character by checking the count of each character in the hash map.

Below is the implementation of the above idea:

C++ ```#include <bits/stdc++.h> using namespace std; char kthNonRepeatingChar(string str, int k) { // Create an empty hash map to store the counts of each // character in the string unordered_map<char, int> charCounts; // Loop through the string and store the counts of each // character in the hash map for (int i = 0; i < str.length(); i++) { charCounts[str[i]]++; } // Loop through the string and find the kth // non-repeating character int nonRepeatingCount = 0; for (int i = 0; i < str.length(); i++) { if (charCounts[str[i]] == 1) { nonRepeatingCount++; if (nonRepeatingCount == k) { // When the count of non-repeating // characters equals k, return the character return str[i]; } } } // If there is no kth non-repeating character in the // string, return the null character return '\0'; } int main() { string str = "geeksforgeeks"; int k = 3; char result = kthNonRepeatingChar(str, k); if (result == '\0') { cout << "There is no kth non-repeating character " "in the string.\n"; } else { cout << "The " << k << "th non-repeating character in the string " "is " << result << ".\n"; } return 0; } ``` Java ```import java.util.*; public class Main { public static char kthNonRepeatingChar(String str, int k) { // Create an empty hash map to store the counts of each // character in the string Map<Character, Integer> charCounts = new HashMap<>(); // Loop through the string and store the counts of each // character in the hash map for (int i = 0; i < str.length(); i++) { char c = str.charAt(i); charCounts.put(c, charCounts.getOrDefault(c, 0) + 1); } // Loop through the string and find the kth // non-repeating character int nonRepeatingCount = 0; for (int i = 0; i < str.length(); i++) { char c = str.charAt(i); if (charCounts.get(c) == 1) { nonRepeatingCount++; if (nonRepeatingCount == k) { // When the count of non-repeating // characters equals k, return the character return c; } } } // If there is no kth non-repeating character in the // string, return the null character return '\0'; } public static void main(String[] args) { String str = "geeksforgeeks"; int k = 3; char result = kthNonRepeatingChar(str, k); if (result == '\0') { System.out.println("There is no kth non-repeating character " + "in the string."); } else { System.out.println("The " + k + "th non-repeating character " + "in the string is " + result + "."); } } } ``` Python ```# Python code of the above approach def kth_non_repeating_char(string, k): # Create an empty dictionary to store # the counts of each character in the string char_counts = {} # Loop through the string and store # the counts of each character in the dictionary for char in string: if char in char_counts: char_counts[char] += 1 else: char_counts[char] = 1 # Loop through the string and find the kth non-repeating character non_repeating_count = 0 for char in string: if char_counts[char] == 1: non_repeating_count += 1 if non_repeating_count == k: # When the count of non-repeating # characters equals k, return the character return char # If there is no kth non-repeating character in the string, return None return None # Main function if __name__ == "__main__": string = "geeksforgeeks" k = 3 result = kth_non_repeating_char(string, k) if result is None: print("There is no kth non-repeating character in the string.") else: print(f"The {k}th non-repeating character in the string is {result}.") # This code is contributed by Susobhan Akhuli ``` C# ```using System; using System.Collections.Generic; class Gfg { static char kthNonRepeatingChar(string str, int k) { // Create a dictionary to store the counts of each character in the string Dictionary<char, int> charCounts = new Dictionary<char, int>(); // Loop through the string and store // the counts of each character in the dictionary foreach (char c in str) { if (charCounts.ContainsKey(c)) { charCounts[c]++; } else { charCounts[c] = 1; } } // Loop through the string and find // the kth non-repeating character int nonRepeatingCount = 0; foreach (char c in str) { if (charCounts[c] == 1) { nonRepeatingCount++; if (nonRepeatingCount == k) { // When the count of non-repeating characters equals k, return the character return c; } } } // If there is no kth non-repeating character in the string, return the null character return '\0'; } static void Main() { string str = "geeksforgeeks"; int k = 3; char result = kthNonRepeatingChar(str, k); if (result == '\0') { Console.WriteLine("There is no kth non-repeating character in the string."); } else { Console.WriteLine(\$"The {k}th non-repeating character in the string is {result}."); } } } ``` JavaScript ```function kthNonRepeatingChar(str, k) { // Create an empty map to store the counts of each // character in the string const charCounts = new Map(); // Loop through the string and store the counts of each // character in the map for (let i = 0; i < str.length; i++) { const char = str[i]; charCounts.set(char, (charCounts.get(char) || 0) + 1); } // Loop through the string and find the kth non-repeating character let nonRepeatingCount = 0; for (let i = 0; i < str.length; i++) { const char = str[i]; if (charCounts.get(char) === 1) { nonRepeatingCount++; if (nonRepeatingCount === k) { // When the count of non-repeating characters equals k, // return the character return char; } } } // If there is no kth non-repeating character in the string, // return the null character return '\0'; } // Main function function main() { const str = "geeksforgeeks"; const k = 3; const result = kthNonRepeatingChar(str, k); if (result === '\0') { console.log("There is no kth non-repeating character in the string."); } else { console.log(`The \${k}th non-repeating character in the string is \${result}.`); } } main(); ```

Output
```The 3th non-repeating character in the string is r.

```

Time Complexity: O(n)
Auxiliary Space: O(n)