HackerRank : Recursive Digit Sum

• 問題URL　https://www.hackerrank.com/challenges/recursive-digit-sum/problem
• 九去法を使用した

#include <bits/stdc++.h>

using namespace std;

vector<string> split_string(string);

// Complete the superDigit function below.

int superDigit(string n, int k) {
    if(k>0){
        long long res=0;
        for(int i=0;i<n.size();i++)res+=n[i]-'0';
        n=to_string(res*k);
        return superDigit(n, 0);
    }else{
        long long res=0;
        for(int i=0;i<n.size();i++){
            res+=(n[i]-'0')%9;
            res%=9;
        }
        return res==0?9:res;
    // cout << "idx:" << idx << "n:" << n.c_str() << boolalpha << isFirst << "\n";
    /* if(n.length()==1)return stoi(n);
    int res=0;
    string temp=n;
    for(int i=1;i<k;i++)n+=temp;
    for(size_t i=0;i<n.length();i++)res+=n[i]-'0';
    n=to_string(res);
    return superDigit(n,0); */
    }
}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    string nk_temp;
    getline(cin, nk_temp);

    vector<string> nk = split_string(nk_temp);

    string n = nk[0];

    int k = stoi(nk[1]);
    
    int result = superDigit(n, k);

    fout << result << "\n";

    fout.close();

    return 0;
}

vector<string> split_string(string input_string) {
    string::iterator new_end = unique(input_string.begin(), input_string.end(), [] (const char &x, const char &y) {
        return x == y and x == ' ';
    });

    input_string.erase(new_end, input_string.end());

    while (input_string[input_string.length() - 1] == ' ') {
        input_string.pop_back();
    }

    vector<string> splits;
    char delimiter = ' ';

    size_t i = 0;
    size_t pos = input_string.find(delimiter);

    while (pos != string::npos) {
        splits.push_back(input_string.substr(i, pos - i));

        i = pos + 1;
        pos = input_string.find(delimiter, i);
    }

    splits.push_back(input_string.substr(i, min(pos, input_string.length()) - i + 1));

    return splits;
}