P1874 快速求和

#include <bits/stdc++.h>

using namespace std;

int f(const string& s, int n, int x, int y, int z) {
	int len = s.size();
	if (x == len) {
		return z == n ? y : INT_MAX;
	}

	int ans = INT_MAX;
	int num = 0;
	for (int i = x; i < len; ++i) {
		num = num * 10 + (s[i] - '0');
		if (num > n) break;
		ans = min(ans, f(s, n, i + 1, y + 1, z + num));
	}
	return ans;
}

int main() {
	string s;
	int n;
	cin >> s >> n;

	int ans = f(s, n, 0, -1, 0);
	if (ans == INT_MAX) {
		cout << -1 << endl;
	} else {
		cout << ans << endl;
	}

	return 0;
}