Find the last non repeating character in string

Given a string str, the task is to find the last non-repeating character in it.
For example, if the input string is “GeeksForGeeks”, then the output should be ‘r’ and if input string is “GeeksQuiz” then the output should be ‘z’. if there is no non-repeating character then print -1.

Examples:

Input: str = “GeeksForGeeks”
Output: r
‘r’ is the first character from the end which has frequency 1.

Input: str = “aabbcc”
Output: -1
All the characters of the given string have frequencies greater than 1.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Create a frequency array which will store the frequency of each of the character of the given string. Once the frequencies have been updated, start traversing the string from the end character by character and for every character, if the frequency of the current character is 1 then this is the last non-repeating character. If all the characters have frequency greater than 1 then print -1.

Below is the implementation of the above approach:

C++

// C++ implementation of the approach 
#include <bits/stdc++.h>  
using namespace std; 
  
// Maximum distinct characters possible 
const int MAX = 256; 
  
// Function to return the last non-repeating character 
static string lastNonRepeating(string str, int n) 
{ 
  
    // To store the frequency of each of 
    // the character of the given string 
    int freq[MAX] = {0}; 
  
    // Update the frequencies 
    for (int i = 0; i < n; i++) 
        freq[str.at(i)]++; 
      
  
    // Starting from the last character 
    for (int i = n - 1; i >= 0; i--)  
    { 
  
        // Current character 
        char ch = str.at(i); 
  
        // If frequency of the current character is 1 
        // then return the character 
        if (freq[ch] == 1) 
        { 
            string res; 
            res+=ch; 
            return res; 
        } 
    } 
  
    // All the characters of the 
    // string are repeating 
    return "-1"; 
} 
  
// Driver code 
int main()  
{ 
    string str = "GeeksForGeeks"; 
    int n = str.size(); 
    cout<< lastNonRepeating(str, n); 
    return 0; 
} 
  
// This code has been contributed by 29AjayKumar 

Java

// Java implementation of the approach 
public class GFG { 
  
    // Maximum distinct characters possible 
    static final int MAX = 256; 
  
    // Function to return the last non-repeating character 
    static String lastNonRepeating(String str, int n) 
    { 
  
        // To store the frequency of each of 
        // the character of the given string 
        int freq[] = new int[MAX]; 
  
        // Update the frequencies 
        for (int i = 0; i < n; i++) 
            freq[str.charAt(i)]++; 
  
        // Starting from the last character 
        for (int i = n - 1; i >= 0; i--) { 
  
            // Current character 
            char ch = str.charAt(i); 
  
            // If frequency of the current character is 1 
            // then return the character 
            if (freq[ch] == 1) 
                return ("" + ch); 
        } 
  
        // All the characters of the 
        // string are repeating 
        return "-1"; 
    } 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        String str = "GeeksForGeeks"; 
        int n = str.length(); 
        System.out.println(lastNonRepeating(str, n)); 
    } 
} 

Python3

# Python3 implementation of the approach  
  
# Maximum distinct characters possible  
MAX = 256;  
  
# Function to return the last non-repeating character  
def lastNonRepeating(string, n) :  
  
    # To store the frequency of each of  
    # the character of the given string  
    freq = [0]*MAX;  
  
    # Update the frequencies  
    for i in range(n) : 
        freq[ord(string[i])] += 1;  
  
    # Starting from the last character  
    for i in range(n-1,-1,-1) : 
  
        # Current character  
        ch = string[i];  
  
        # If frequency of the current character is 1  
        # then return the character  
        if (freq[ord(ch)] == 1) : 
            return ("" + ch);  
      
  
    # All the characters of the  
    # string are repeating  
    return "-1";  
  
  
# Driver code  
if __name__ == "__main__" :  
      
    string = "GeeksForGeeks";  
    n = len(string);  
      
    print(lastNonRepeating(string, n));  
  
# This code is contributed by AnkitRai01 

C#

// C# implementation of the approach 
using System; 
      
class GFG  
{ 
  
    // Maximum distinct characters possible 
    static readonly int MAX = 256; 
  
    // Function to return the last non-repeating character 
    static String lastNonRepeating(String str, int n) 
    { 
  
        // To store the frequency of each of 
        // the character of the given string 
        int []freq = new int[MAX]; 
  
        // Update the frequencies 
        for (int i = 0; i < n; i++) 
            freq[str[i]]++; 
  
        // Starting from the last character 
        for (int i = n - 1; i >= 0; i--)  
        { 
  
            // Current character 
            char ch = str[i]; 
  
            // If frequency of the current character is 1 
            // then return the character 
            if (freq[ch] == 1) 
                return ("" + ch); 
        } 
  
        // All the characters of the 
        // string are repeating 
        return "-1"; 
    } 
  
    // Driver code 
    public static void Main(String[] args) 
    { 
        String str = "GeeksForGeeks"; 
        int n = str.Length; 
        Console.WriteLine(lastNonRepeating(str, n)); 
    } 
} 
  
/* This code contributed by PrinciRaj1992 */

Output:

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

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