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Count the number of unique characters in a given String

  • Last Updated : 17 Jan, 2022

Given a string, str consisting of lowercase English alphabets, the task is to find the number of unique characters present in the string.

Examples:

Input: str = “geeksforgeeks”
Output: 7
Explanation: The given string “geeksforgeeks” contains 7 unique characters {‘g’, ‘e’, ‘k’, ‘s’, ‘f’, ‘o’, ‘r’}.

Input: str = “madam”
Output: 3

 

Approach: The given problem can be solved using the set data structure. The idea is to initialize an unordered set that stores all the distinct characters of the given string. The size of the set after the string is traversed is the required answer.

Below is the implementation of the above approach:

C++




// C++ program of the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Program to count the number of
// unique characters in a string
int cntDistinct(string str)
{
    // Set to store unique characters
    // in the given string
    unordered_set<char> s;
 
    // Loop to traverse the string
    for (int i = 0; i < str.size(); i++) {
 
        // Insert current character
        // into the set
        s.insert(str[i]);
    }
 
    // Return Answer
    return s.size();
}
 
// Driver Code
int main()
{
    string str = "geeksforgeeks";
    cout << cntDistinct(str);
 
    return 0;
}

Java




// Java program of the above approach
import java.util.*;
 
class GFG{
 
// Program to count the number of
// unique characters in a string
static int cntDistinct(String str)
{
     
    // Set to store unique characters
    // in the given string
    HashSet<Character> s = new HashSet<Character>();
 
    // Loop to traverse the string
    for(int i = 0; i < str.length(); i++)
    {
         
        // Insert current character
        // into the set
        s.add(str.charAt(i));
    }
 
    // Return Answer
    return s.size();
}
 
// Driver Code
public static void main(String args[])
{
    String str = "geeksforgeeks";
    System.out.print(cntDistinct(str));
}
}
 
// This code is contributed by sanjoy_62

Python3




# Python 3 program of the above approach
 
# Program to count the number of
# unique characters in a string
def cntDistinct(st):
 
    # Set to store unique characters
    # in the given string
    s = set([])
 
    # Loop to traverse the string
    for i in range(len(st)):
 
        # Insert current character
        # into the set
        s.add(st[i])
 
    # Return Answer
    return len(s)
 
# Driver Code
if __name__ == "__main__":
 
    st = "geeksforgeeks"
    print(cntDistinct(st))
 
    # This code is contributed by ukasp.

C#




// C# program to implement
// the above approach
using System;
using System.Collections.Generic;
 
class GFG
{
 
// Program to count the number of
// unique characters in a string
static int cntDistinct(string str)
{
     
    // Set to store unique characters
    // in the given string
    HashSet<char> s = new HashSet<char>();
 
    // Loop to traverse the string
    for(int i = 0; i < str.Length; i++)
    {
         
        // Insert current character
        // into the set
        s.Add(str[i]);
    }
 
    // Return Answer
    return s.Count;
}
 
// Driver Code
public static void Main()
{
    string str = "geeksforgeeks";
    Console.Write(cntDistinct(str));
}
}
 
// This code is contributed by Samim Hossain Mondal.

Javascript




<script>
      // JavaScript code for the above approach
 
      // Program to count the number of
      // unique characters in a string
      function cntDistinct(str)
      {
       
          // Set to store unique characters
          // in the given string
          let s = new Set();
 
          // Loop to traverse the string
          for (let i = 0; i < str.length; i++) {
 
              // Insert current character
              // into the set
              s.add(str[i]);
          }
 
          // Return Answer
          return s.size;
      }
 
      // Driver Code
 
      let str = "geeksforgeeks";
      document.write(cntDistinct(str));
 
// This code is contributed by Potta Lokesh
  </script>
Output
7

Time Complexity: O(N)
Auxiliary space: O(1)

 


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