# K’th Non-repeating Character

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 ``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 + ``"."``);``        ``}``    ``}``}`

## Python3

 `# 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 ``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 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 + ``"."``);``        ``}``    ``}``}`

## Python3

 `# 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++;``            ``}``            ``else``            ``{``                ``charCounts = 1;``            ``}``        ``}` `        ``// Loop through the string and find``      ``// the kth non-repeating character``        ``int` `nonRepeatingCount = 0;``        ``foreach` `(``char` `c ``in` `str)``        ``{``            ``if` `(charCounts == 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(1)