Solve the Frequent Words Problem

/**
 * Input: A string Text and an integer k.
 * Output: All most frequent k-mers in Text.
 */

#include <iostream>  // std::cout, std::endl
#include <string>    // std::string
#include <map>       // std::map
#include <algorithm> // std::find

using std::map;
using std::string;
using std::find;
using std::cout;
using std::endl;

int main() {
    int length = 4;
    string input = "ACGTTGCATGTCGCATGATGCATGAGAGCT";

    map<string, int> array;

    for (int pos = 0; pos < input.length() - length; ++pos) {
        string substr = input.substr(pos, length);

        auto search = array.find(substr);

        // Если строка уже встречалась в тексте
        if (search != array.end()) {
            search->second += 1;
        }else {
            array[substr] = 1;
        }
    }

    int max = 0;
    for (auto &substr : array) {
        if (max < substr.second) {
            max = substr.second;
        }
    }

    for (auto &substr : array) {
        if (max == substr.second) {
            cout << substr.first << " ";
        }
    }


    return 0;
}