백준 1038번 C++ 풀이

#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;
long long radix_global;
bool decreasing(long long n){
    if (n < 10){
        return true;
    }
    int last = n % 10;
    n = n / 10;
    int next_last = n % 10;
    int radix = 1;
    while (n != 0 ){
        radix *= 10;
        if (next_last <= last){
            radix_global = radix;
            return false;
        }
        last = next_last;
        n = n / 10;
        next_last = n% 10;
    }
    return true;

}
int main(){
    cin.tie(NULL);
    ios::sync_with_stdio(false);
    long long n;

    cin >> n;
    long long index = 0;
    long long number = -1;
    if (n > 1022){
        cout << -1;
        return 0;
    }
    while (number != n){
//        cout << index << '\n';

        if (decreasing(index)) {

            number++;
            index++;
        }else {
            index /= radix_global;
            index *= radix_global;
            index += radix_global;

        }
    }
    cout << index-1;

//    cout << decreasing(10);
    return 0;

}