string Compile(const string& code) {
string str(code);
typedef pair<char, int> ci;
stack<ci> St;
FOR (i, str.length()) {
const char c = str[i];
if (c == '<') {
St.push(ci(c, i));
}
else if (c == '>') {
if (!St.empty()) {
const int beginIdx = St.top().second + 1;
string sub = str.substr(beginIdx, (i - beginIdx));
sub = RollOut(sub);
string prev(str.substr(0, beginIdx-1));
string post(str.substr(i+1, str.length()-(i+1)));
str = prev + sub + post;
St.pop();
}
else {
return "Error: not paired!";
}
}
else {}
}
return str;
}
string RollOut(const string& str) {
const auto it = begin(str);
const auto itLast = find_if(it, end(str), [](const char c){
return isalpha(c);
});
const int dist = distance(it, itLast);
const string strNum = str.substr(0, dist);
const int num = stoi(strNum);
const int trL = str.length() - dist;
const string trStr = str.substr(dist, trL);
string result("");
FOR (i, num) {
result += trStr;
}
return result;
}
