lowest.cpp

#include<iostream>
#include<string>
#include<algorithm>
std::string lowest_number(std::string str, int k) {

        std::string res="";

    if (k == 0){
        res.append(str);
        return res;
    }



    if (str.length() <= k)
        return res;



    int min = 0;
    for (int i = 1; i<=k ; i++)
        if (str[i] < str[min])
            min = i;


    res+=str[min];


    return res + lowest_number(str.substr(min+1), k-min);
}



int main()
{
    std::string str = "100100111",res="";
    int k = 2;
    res = lowest_number(str, k);

        size_t pos=0;

        for(size_t i=0;i<res.length();i++){
           if(res[i]=='0') pos++;
           else break;
        }

        res.erase(0,pos);

        std::cout<<res;
    return 0;
}