https://www.acmicpc.net/problem/16943
순열 함수(next_permutation) 이용하면 so easy~
※ 0으로 시작하면 안된다는 조건 주의
#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>
using namespace std;
int main() {
string A,B;
int tmp=0, result=-1;
cin >> A >> B;
sort(A.begin(), A.end());
do {
tmp = stoi(A);
if(tmp < stoi(B) && tmp > result)
result = tmp;
} while(next_permutation(A.begin(), A.end()));
if(result < pow(10, A.size()-1))
result = -1;
cout << result << endl;
return 0;
}