B8DK14 - Online C++0x Compiler & Debugging Tool

#include<bits/stdc++.h>
#define f1(i, n) for(ll i=1;i<=n;++i)
#define f0(i, n) for(ll i=0;i<n;++i)
#define ull unsigned long long
#define ll long long
#define rev(a) reverse(a.begin(),a.end())
#define all(x) x.begin(),x.end()
#define so(A, n) sort(A+1, A+n+1)
using namespace std;
const int maxn = 200010;
const int N = 1e5 + 1;
// Duyet trau
void c1() {
	int n;
	string s;
	cin >> n >> s;
	bool ch['9' + 1] = {};
	int cnt = 0;
	for (int i = 0; i < s.size(); ++i) ch[s[i]] = true;
	for (int i = 1; i <= n; ++i) {
		string a = to_string(i);
		bool check = true;
		for (int j = 0; j < a.size(); ++j) {
			if (ch[a[j]]) {
				check = false;
				break;
			}
		}
		if (!check) cnt++;
	}
	cout << n - cnt;
}
// Backtracking
vector<int> v;
int ans = 0, n, cnt = 0;
int countDigit(int n) {
	int res = 0;
	while (n != 0) {n /= 10; ++res;}
	return res;
}
set<int> result;
void backtrack(int pos, int uia) {
	if (pos > uia) {
		return;
	}
	for (int i = 0; i < v.size(); ++i) {
		ans = ans * 10 + v[i];
		if (ans <= n && ans != 0) {
			result.insert(ans);
		}
		backtrack(pos + 1, uia);
		ans /= 10;
	}
}
int main()
{
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	string s;
	cin >> n >> s;
	for (int i = 0; i <= 9; ++i) {
		v.push_back(i);
		for (int j = 0; j < s.size(); ++j) {if (s[j] - 48 == i) {v.pop_back(); break;}}
	}
	int motcaigiday = countDigit(n);
	backtrack(1, motcaigiday);
	cout << result.size() << "\n";
	return 0;
}