排列型递归应用

#include <bits/stdc++.h>

using namespace std;

int v[10], p[10], n, ans;

int get(int l, int r) {
    int num = 0;
    for (int i = r; i >= l; --i) num = num * 10 + p[i];
    return num;
}

void dfs(int t) {
    if (t > 9) {
        for (int i = 1; i <= 7; ++i) {
            int a = get(1, i);
            for (int j = 1; j < 9 - i; ++j) {
                int k = get(i + 1, i + j);
                int m = get(i + j + 1, 9);
                if (k % m == 0 && a + k / m == n) ans++;
            }
        }
        return;
    }
    for (int i = 1; i <= 9; ++i) {
        if (v[i] == 0) {
            v[i] = 1, p[t] = i;
            dfs(t + 1);
            v[i] = 0;
        }
    }
}

int main() {
    cin >> n;
    dfs(1);
    cout << ans << endl;
    return 0;
}