计算给定字符串中唯一字符的数量

给定一个由小写英文字母组成的字符串str ，任务是找出字符串中存在的唯一字符的数量。

例子：

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

方法：给定的问题可以使用集合数据结构来解决。这个想法是初始化一个存储给定字符串的所有不同字符的无序集。遍历字符串后的集合大小就是必填答案。

下面是上述方法的实现：

C++

// C++ program of the above approach
#include 
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 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 s = new HashSet();
 
    // 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 s = new HashSet();
 
    // 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

      // 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
  

输出

7

时间复杂度： O(N)
辅助空间： O(1)