USACO 2.2 Runaround Numbers

Straight forward brutal force approach. Mainly test implementation skills.

#include <algorithm>
#include <vector>
#include <iostream>
#include <fstream>
#include <set>
#include <unordered_map>

using namespace std;

int N;

bool isRunaroundNumber(int n) {
    vector<int> num;
    unordered_map<int, int> map;
    while (n) {
        int d = n % 10;
        if (map.find(d) != map.end()) {
            return false;
        }
        map[d] = 0;
        num.push_back(d);
        n /= 10;
    }

    reverse(num.begin(), num.end());
    int size = (int)num.size(), index = 0, next = -1;
    map[num[0]] = 1;

    while (next != 0) {
        int next = (index + num[index]) % size;
        if (next == 0) {
            for (int i = 0; i < size; ++i) {
                if (map[num[i]] != 1)
                    return false;
            }
            return true;
        }
        if (map[num[next]] == 1)
            return false;
        map[num[next]]++;
        index = next;
    }
    return false;
}

int main() {
    ifstream fin("runround.in");
    ofstream fout("runround.out");
    fin >> N;
    ++N;
    while (!isRunaroundNumber(N++));
    fout << --N << endl;
}