暴力DFS，11跑起來就很吃力了。

#include <iostream>
#include <string>
using namespace std;

#define N 11
int res = 0;
void dfs(string help,int k,int cnt) {
    if (cnt == N) {
        res++;
        /*while (help[0] == ‘0‘&&help.length() > 1) {
            help.erase(help.begin());
        }
        cout << help<<endl;
 
*/
        return;
    }
    if (k == 10)return;
    for (int i = 0; i <= N - cnt; i++ ) {
        dfs(help + string(i, k + ‘0‘), k + 1, cnt + i);
    }
}

int main() {
    dfs("",0,0);
    cout << res << endl;
    return 0;
}

隨手記——獲取N位唯一數（不同排列123,321,213都算同一個）