Least

#include<iostream>
using namespace std;
void buildLowestNumberRec(string str, int n, string &res)
{
	if (n == 0)
	{
		res.append(str);
		return;
	}

	int len = str.length();
	if (len <= n)
		return;
	int minIndex = 0;
	for (int i = 1; i<=n ; i++)
		if (str[i] < str[minIndex])
			minIndex = i;
	res.push_back(str[minIndex]);
	string new_str = str.substr(minIndex+1, len-minIndex);
	buildLowestNumberRec(new_str, n-minIndex, res);
}
string buildLowestNumber(string str, int n)
{
	string res = "";
	buildLowestNumberRec(str, n, res);
	return res;
}
int main()
{
	string str = "121198";
	int n = 2;
	cout << buildLowestNumber(str, n);
	return 0;
}