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Frequency of each character in a String using unordered_map in C++
  • Difficulty Level : Basic
  • Last Updated : 26 Oct, 2020

Given a string str, the task is to find the frequency of each character of a string using an unordered_map in C++ STL.

Examples: 

Input: str = “geeksforgeeks” 
Output: 
r 1 
e 4 
s 2 
g 2 
k 2 
f 1 
o 1

Input: str = “programming” 
Output: 
n 1 
i 1 
p 1 
o 1 
r 2 
a 1 
g 2 
m 2 

Approach: 



  1. Traverse each character of the given string str.
  2. Check whether the current character is present in unordered_map or not.
  3. If it is present, then update the frequency of the current characters else insert the characters with frequency 1 as shown below: 
if(M.find(s[i])==M.end()) {
    M.insert(make_pair{s[i], 1});
}
else {
    M[s[i]]++;
}

        4. Traverse the unordered_map and print the frequency of each characters stored as a mapped value.

Below is the implementation of the above approach:

CPP




// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
 
void printFrequency(string str)
{
    // Define an unordered_map
    unordered_map<char, int> M;
 
    // Traverse string str check if
    // current character is present
    // or not
    for (int i = 0; str[i]; i++)
    {
        // If the current characters
        // is not found then insert
        // current characters with
        // frequency 1
        if (M.find(str[i]) == M.end())
        {
            M.insert(make_pair(str[i], 1));
        }
 
        // Else update the frequency
        else
        {
            M[str[i]]++;
        }
    }
 
    // Traverse the map to print the
    // frequency
    for (auto& it : M) {
        cout << it.first << ' ' << it.second << '\n';
    }
}
 
// Driver Code
int main()
{
    string str = "geeksforgeeks";
 
    // Function call
    printFrequency(str);
    return 0;
}
Output
r 1
e 4
s 2
g 2
k 2
f 1
o 1
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