Find frequency of all characters in a string in C++

This post will discuss how to find the frequency of all characters in a string in C++.

A simple and efficient solution is to create a frequency map. The idea is to iterate the string using std::for_each or range-based for-loop, and for each character, insert/update its count into a map. This works in linear time and takes space proportional to the total number of distinct characters present in the string.

1. Using `std::for_each` function

#include <unordered_map>

#include <algorithm>

#include <string>

#include <iostream>

int main()

{

std::string str = "techiedelight";

std::unordered_map<char, int> freq;

std::for_each(std::begin(str),

std::end(str),

[&freq](const char &c) {

freq[c]++;

});

for (auto &pair: freq) {

std::cout << '{' << pair.first << ": " << pair.second << '}' << std::endl;

}

return 0;

}

Download Run Code

Output:

{g: 1}
{l: 1}
{d: 1}
{i: 2}
{t: 2}
{e: 3}
{c: 1}
{h: 2}

2. Using Range-based for-loop