K'th Non-repeating Character
Last Updated :
15 Jul, 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;
}
// 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 + ".");
}
}
}
# 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
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
// 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}`);
}
OutputThe 3th non-repeating character in the string is r.
Time Complexity: O(n²)
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;
}
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 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
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}.");
}
}
}
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();
OutputThe 3th non-repeating character in the string is r.
Time Complexity: O(n)
Auxiliary Space: O(n)
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