Подсчёт слов в предложении, оканчивающиеся на разные буквы

#include <iostream>
#include <unordered_map>
#include <string>
#include <regex>
#include <algorithm>
 
int main()
{
    std::unordered_map<std::string, int>diffLett{};
    const std::string sentence{"I have problems in solving this problem: count how many times in each sentence there are words ending in different letters."};
    std::regex reg{R"((?:^|[\s\W]*)(?:[\w\d]*)(\w|d)[[:punct:]]?(?=$|[\s\W\D]*))"};
    for(auto it=std::sregex_iterator{sentence.begin(), sentence.end(), reg}; it!=std::sregex_iterator{}; it++)
    {
        diffLett[it->str(1)]++;
    }
    
    std::cout<<count_if(diffLett.cbegin(), diffLett.cend(), [](const std::pair<const std::string,int> &p){
        return p.second==1;
    });
}

#include <iostream>
#include <sstream>
#include <unordered_map>
#include <string>
#include <algorithm>
#include <iterator>
 
int main()
{
    std::unordered_map<char, int>diffLett{};
    const std::string sentence{"I have problems in solving this problem: count how many times in each sentence there are words ending in different letters."};
    std::stringstream sbuf{sentence};
    for_each(std::istream_iterator<std::string>(sbuf),{},[&diffLett](const std::string & str){
        if(ispunct(str.back())){
            diffLett[str[str.length()-2]]++;
        } else  diffLett[str.back()]++;
    });
    
    std::cout<<count_if(diffLett.cbegin(), diffLett.cend(), [](const std::pair<const char,int> &p){
        return p.second==1;
    });
}